Archive for March, 2012
MySQL REGEXP Error
While working through prepared statements in MySQL, there was an interesting MySQL regular expression question raised. A student wanted to know how to address the following error message:
ERROR 1139 (42000): Got error 'repetition-operator operand invalid' FROM REGEXP |
They had substituted * for a .+ in a metasequence. A metasequence is a parenthetical expression that evaluates based on multiple alternative conditions, and the pipe (|) acts as an OR operator. The full code example is found on page 482 of the Oracle Database 11g & MySQL 5.6 Developer Handbook. The student’s change would have worked without an error had he replaced the metasequence with .* instead of the solitary *.
The original call to the procedure passes the following well formed regular expression:
CALL prepared_dml('(^|^.+)war(.+$|$)'); |
Or, they could eliminate the metasequences and use:
CALL prepared_dml('^.*war.*$'); |
Either returns the following entries from a column with movie titles from the sample code:
Charlie's War Star Wars I Star Wars II Star Wars III |
The dot (.) means any possible character, and the plus (+) means one-to-many possible repeating characters of a preceding character. When the dot precedes the plus, it means one-to-many wildcard characters. The student replaced the metasequence with an asterisk by itself and generated the badly formed regular expression error.
The misunderstanding occurs because the asterisk (*) by itself doesn’t mean zero-to-many wildcard. The combination of the dot and asterisk creates a zero-to-many wildcard, which works when there is or isn’t a character before the first character of a string or after the last character of a string. It also eliminates the need for a metasequence.
Here’s a small test case outside of the book’s stored procedure:
-- Conditionally drop the table. DROP TABLE IF EXISTS list; -- Create the table. CREATE TABLE list ( list_id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT, list_item VARCHAR(20)); -- Insert for rows. INSERT INTO list (list_item) VALUES ('Star'),(' Star'),(' Star '),('Star '); -- Query for zero-to-many leading characters. SELECT list_id AS "ID" , list_item AS "Zero-to-many leading characters " , LENGTH(list_item) AS "Length" , '^.*Star.*$' AS "Regular Expression" FROM list WHERE list_item REGEXP '^.*Star.*$'; -- Query for zero-to-many leading characters. SELECT list_id AS "ID" , list_item AS "One-to-many leading characters " , LENGTH(list_item) AS "Length" , '^.+Star.*$' AS "Regular Expression" FROM list WHERE list_item REGEXP '^.+Star.*$'; -- Query for one-to-many leading characters. SELECT list_id AS "ID" , list_item AS "Zero-to-many trailing characters" , LENGTH(list_item) AS "Length" , '^.*Star.*$' AS "Regular Expression" FROM list WHERE list_item REGEXP '^.*Star.*$'; -- Query for one-to-many leading characters. SELECT list_id AS "ID" , list_item AS "One-to-many trailing characters " , LENGTH(list_item) AS "Length" , '^.*Star.+$' AS "Regular Expression" FROM list WHERE list_item REGEXP '^.*Star.+$'; |
The output from the scripts is:
+----+----------------------------------+--------+--------------------+ | ID | Zero-to-many leading characters | Length | Regular Expression | +----+----------------------------------+--------+--------------------+ | 1 | Star | 4 | ^.*Star.*$ | | 2 | Star | 5 | ^.*Star.*$ | | 3 | Star | 6 | ^.*Star.*$ | | 4 | Star | 5 | ^.*Star.*$ | +----+----------------------------------+--------+--------------------+ 4 rows in set (0.02 sec) +----+----------------------------------+--------+--------------------+ | ID | One-to-many leading characters | Length | Regular Expression | +----+----------------------------------+--------+--------------------+ | 2 | Star | 5 | ^.+Star.*$ | | 3 | Star | 6 | ^.+Star.*$ | +----+----------------------------------+--------+--------------------+ 2 rows in set (0.00 sec) +----+----------------------------------+--------+--------------------+ | ID | Zero-to-many trailing characters | Length | Regular Expression | +----+----------------------------------+--------+--------------------+ | 1 | Star | 4 | ^.*Star.*$ | | 2 | Star | 5 | ^.*Star.*$ | | 3 | Star | 6 | ^.*Star.*$ | | 4 | Star | 5 | ^.*Star.*$ | +----+----------------------------------+--------+--------------------+ 4 rows in set (0.02 sec) +----+----------------------------------+--------+--------------------+ | ID | One-to-many trailing characters | Length | Regular Expression | +----+----------------------------------+--------+--------------------+ | 3 | Star | 6 | ^.*Star.+$ | | 4 | Star | 5 | ^.*Star.+$ | +----+----------------------------------+--------+--------------------+ 2 rows in set (0.02 sec) |
Hope this helps.
Oracle CSV Imports
The first step in creating an effective import plan for comma-separated value (CSV) files is recognizing your options in a database. There are several options in an Oracle database. You can read the file with Java, C/C++, C#, PL/SQL (through the UTL_FILE package), PHP, Perl, or any other C-callable programming language; or you can use SQL*Loader as a standalone utility or through externally managed tables (known as external tables). The most convenient and non-programming solution is using external tables.
Adopting external tables as your import solution should drive you to consider how to manage the security surrounding this type of methodology. Host hardening is a critical security step because it shuts down most, hopefully all, unauthorized use of the operating system where the database and external files reside. Next, you need to manage the access to the external tables and ensure that exposure of business sensitive information in CSV files is minimized.
This post explains how to manage access and police (cleanup external files) once they’re read into the database. It assumes you have root-level permissions to the operating system and database. The SYS and SYSTEM accounts have the equivalent of root permissions for database configuration. The rule of thumb with these accounts is simple, manage as much as possible with the SYSTEM account before you use the SYS account.
Setting up the Import File System
While you can do all the setup of virtual directories in Oracle regardless of whether you’ve set them up in the operating system, it’s a good idea to set them up in the OS first. The example is using a Windows 7 OS, so you’ll need to change the directories when working in Linux or Unix. Here are the directories:
C:\Imports\ImportFiles C:\Imports\ImportLogs |
You may take note that there are two directories. That’s because you don’t want to grant write privileges to the Oracle virtual directory where you put the files. You can grant read-only privileges to the virtual directory and read-write privileges to the log directory.
Setting up the Import User/Schema
This step lets you create an IMPORT user/schema in the Oracle database. You need to connect as the SYSTEM user to perform these steps (or another authorized DBA account with adequate privileges):
CREATE USER import IDENTIFIED BY import DEFAULT TABLESPACE users QUOTA 1000M ON users TEMPORARY TABLESPACE temp; |
After creating the user, grant the privileges like this as the SYSTEM user:
GRANT CREATE CLUSTER, CREATE INDEXTYPE, CREATE OPERATOR , CREATE PROCEDURE, CREATE SEQUENCE, CREATE SESSION , CREATE SYNONYM, CREATE TABLE, CREATE TRIGGER , CREATE TYPE, CREATE VIEW TO import; |
Setting up Virtual Directories
A virtual directory in Oracle acts maps an internal database directory name (known as a virtual directory) to a physical directory of the operating system. You create two virtual directories in this example, one holds read-only permissions to the directory where you’re putting the data file, and the other holds read-write permissions to the directory where you’re writing any log files from the external file process.
Log files are generated from this process when you query the data from the external file. Any error in the files conformity is written to a log file.
CREATE DIRECTORY upload_files AS 'C:\Imports\ImportFiles'; CREATE DIRECTORY upload_logs AS 'C:\Imports\ImportLogs'; |
After creating the virtual directories in the database, you must grant appropriate access to the user account that will access the data. This grants those permissions to the IMPORT user:
GRANT READ ON DIRECTORY upload_files TO import; GRANT READ, WRITE ON DIRECTORY upload_logs TO import; |
Setting up an External Table
An external table references both the UPLOAD_FILES and UPLOAD_LOGS virtual directories, and the virtual directories must map to physical directories that allow read and write privileges to the Oracle user. Here’s the external table for this example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | CREATE TABLE item_import_ext_table ( asin_number VARCHAR2(10) , item_type VARCHAR2(15) , item_title VARCHAR2(60) , item_subtitle VARCHAR2(60) , item_rating VARCHAR2(8) , item_rating_agency VARCHAR2(4) , item_release_date DATE) ORGANIZATION EXTERNAL ( TYPE oracle_loader DEFAULT DIRECTORY upload_files ACCESS PARAMETERS ( RECORDS DELIMITED BY NEWLINE CHARACTERSET US7ASCII BADFILE 'UPLOAD_LOGS':'item_import_ext_table.bad' DISCARDFILE 'UPLOAD_LOGS':'item_import_ext_table.dis' LOGFILE 'UPLOAD_LOGS':'item_import_ext_table.log' FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY "'" MISSING FIELD VALUES ARE NULL ) LOCATION ('item_import.csv')) REJECT LIMIT UNLIMITED; |
Setting up a Physical File
You should put the following in a item_import.csv physical file (case sensitivity won’t matter on the Windows 7 platform but will matter on the Linux or Unix platforms):
'B000W74EQC','DVD_WIDE_SCREEN','Harry Potter and the Sorcerer''s Stone',,'PG','MPAA','11-DEC-2007' 'B000W746GK','DVD_WIDE_SCREEN','Harry Potter and the Chamber of Secrets',,'PG','MPAA','11-DEC-2007' 'B000W796OM','DVD_WIDE_SCREEN','Harry Potter and the Prisoner of Azkaban',,'PG','MPAA','11-DEC-2007' 'B000E6EK2Y','DVD_WIDE_SCREEN','Harry Potter and the Goblet of Fire',,'PG-13','MPAA','07-MAR-2006' 'B000W7F5SS','DVD_WIDE_SCREEN','Harry Potter and the Order of the Phoenix',,'PG-13','MPAA','11-DEC-2007' 'B002PMV9FG','DVD_WIDE_SCREEN','Harry Potter and the Half-Blood Prince',,'PG','MPAA','08-DEC-2009' 'B001UV4XHY','DVD_WIDE_SCREEN','Harry Potter and the Deathly Hallows, Part 1',,'PG-13','MPAA','15-APR-2011' 'B001UV4XIS','DVD_WIDE_SCREEN','Harry Potter and the Deathly Hallows, Part 2',,'PG-13','MPAA','11-NOV-2011' |
Testing the External Table
After putting the item_import.csv file in the C:\Imports\ImportFiles directory, you can test the process at this point by running the following query:
SET PAGESIZE 99 COLUMN asin_number FORMAT A11 HEADING "ASIN #" COLUMN item_title FORMAT A46 HEADING "ITEM TITLE" COLUMN item_rating FORMAT A6 HEADING "RATING" COLUMN item_release_date FORMAT A11 HEADING "RELEASE|DATE" SELECT asin_number , item_title , item_rating , TO_CHAR(item_release_date,'DD-MON-YYYY') AS item_release_date FROM item_import_ext_table; |
It should return eight rows.
Extending Access to the Data Dictionary
The physical directory names of virtual directories are hidden from generic users. They’re available in the ALL_DIRECTORIES and DBA_DIRECTORIES administrative view for queries by the SYS, SYSTEM, and any DBA role privileged users.
While a privileged user can query the view, placing the view inside a function or procedure deployed in the privileged user’s schema would raise an ORA-00942 error. That error signals that the table or view does not exist.
This example deploys the view in the SYSTEM schema. That means it requires you make the following grant as the SYS user:
GRANT SELECT ON sys.dba_directories TO system; |
After making the grant from the SYS schema to the SYSTEM schema, connect to the SYSTEM schema. Then, create the following GET_DIRECTORY_PATH function:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | CREATE OR REPLACE FUNCTION get_directory_path ( virtual_directory IN VARCHAR2 ) RETURN VARCHAR2 IS -- Define RETURN variable. directory_path VARCHAR2(256) := ''; --Define dynamic cursor. CURSOR get_directory (virtual_directory VARCHAR2) IS SELECT directory_path FROM sys.dba_directories WHERE directory_name = virtual_directory; -- Define a LOCAL exception FOR name violation. directory_name EXCEPTION; PRAGMA EXCEPTION_INIT(directory_name,-22284); BEGIN OPEN get_directory (virtual_directory); FETCH get_directory INTO directory_path; CLOSE get_directory; -- RETURN file name. RETURN directory_path; EXCEPTION WHEN directory_name THEN RETURN NULL; END get_directory_path; / |
It’s tempting to make the grant on this function to PUBLIC user but that would expose information that any DBA should try and limit. That means you grant EXECUTE privilege only to the IMPORT schema.
This grant should be made as the SYSTEM user:
GRANT EXECUTE ON get_directory_path TO import; |
After granting the EXECUTE privilege to the IMPORT user, connect to the IMPORT schema and create a synonym to the GET_DIRECTORY_PATH function. The syntax for that command is:
CREATE SYNONYM get_directory_path FOR system.get_directory_path; |
You can now test your access to the function with the following query from the IMPORT schema:
SELECT get_directory_path('UPLOAD_FILES') FROM dual; |
You should return the following if you’ve got everything working at this point:
GET_DIRECTORY_PATH('UPLOAD_FILES')
------------------------------------
C:\Imports\ImportFiles |
At this point, you’ve completed the second major configuration component. You now need the ability to read files outside the database, which can be done with Java in Oracle 10g or Oracle 11g (that’s not possible in Oracle 10g XE or Oracle 11g XE because they don’t support an internal JVM). The
Reading Virtual Directory Files
The GET_DIRECTORY_PATH function provides you with the ability to read the Oracle data catalog and find the absolute directory path of a virtual directory. In this framework, you need this value to find whether the item_import.csv physical file is present in the file system before you read the file.
There doesn’t appear to be a neat little function to read an external directory. At least, there’s not one in the UTL_FILE or DBMS_LOB packages where you’d think it should be found. Unfortunately, that leaves us with two alternatives. One is to write an external library in C, C++, or C#. Another is to write an internal Java library that reads the file system. You accomplish this by granting permissions to a target directory or directories.
The first step is to create a scalar array of VARCHAR2 variables, like
CREATE OR REPLACE TYPE file_list AS TABLE OF VARCHAR2(255); / |
The second step is to write the Java library file. You can write it three ways. One accepts default error handling and the others override the default exception handling. If you’re new to Java, you should take the basic library with default handling. If you’ve more experience, you may want to override the helpful message with something that causes the developer to check with the DBA or simply suppress the message to enhance security.
You should note that the database connection is an Oracle Database 11g internal database connection. The connection only does one thing. It allows you to map the ArrayDescriptor to a schema-level SQL collection type. The element types of these collections should be scalar variables, like DATE, NUMBER, or VARCHAR2 data types.
The more advanced method overrides exception handling by suppressing information about the java.properties settings. You can do it by catching the natively thrown exception and re-throw it or ignore it. The example ignores it because handling it in Java reports an unhandled exception at the PL/SQL or SQL layer, which leads end users to think you have a major design problem.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 | CREATE OR REPLACE AND COMPILE JAVA SOURCE NAMED "ListVirtualDirectory" AS // Import required classes. import java.io.*; import java.security.AccessControlException; import java.sql.*; import java.util.Arrays; import oracle.sql.driver.*; import oracle.sql.ArrayDescriptor; import oracle.sql.ARRAY; // Define the class. public class ListVirtualDirectory { // Define the method. public static ARRAY getList(String path) throws SQLException { // DECLARE variable AS a NULL, required because OF try-catch block. ARRAY listed = NULL; // Define a connection (this IS FOR Oracle 11g). Connection conn = DriverManager.getConnection("jdbc:default:connection:"); // USE a try-catch block TO trap a Java permission error ON the directory. try { // DECLARE a class WITH the file list. File directory = NEW File(path); // DECLARE a mapping TO the schema-level SQL collection TYPE. ArrayDescriptor arrayDescriptor = NEW ArrayDescriptor("FILE_LIST",conn); // Translate the Java String[] TO the Oracle SQL collection TYPE. listed = NEW ARRAY(arrayDescriptor,conn,((Object[]) directory.list())); } catch (AccessControlException e) {} RETURN listed; }} / |
You can’t call an internal Java library without a PL/SQL wrapper function. Here’s the wrapper function for this Java library:
CREATE OR REPLACE FUNCTION list_files(path VARCHAR2) RETURN FILE_LIST IS LANGUAGE JAVA NAME 'ListVirtualDirectory.getList(java.lang.String) return oracle.sql.ARRAY'; / |
You MUST grant the Oracle Database’s internal JVM authority to read the external directory before you can return the directory contents. Any attempt to read a directory without the proper permissions raises an ORA-29532 exception.
The following is an anonymous block to grant permissions to a directory. You must grant a minimum of read permissions but since you’ll also delete this file later in the post you should grant read, write, and delete. You must run it from the SYSDBA role as the SYS user.
1 2 3 4 5 6 7 | BEGIN DBMS_JAVA.GRANT_PERMISSION('IMPORT' ,'SYS:java.io.FilePermission' ,'C:\Imports\ImportFiles' ,'read,write,delete'); END; / |
While you’re connected, it’s a good idea to grant the same privileges to your log directory:
1 2 3 4 5 6 7 | BEGIN DBMS_JAVA.GRANT_PERMISSION('IMPORT' ,'SYS:java.io.FilePermission' ,'C:\Imports\ImportLogs' ,'read,write,delete'); END; / |
You should now be able to read the contents of an external file from another PL/SQL block or from a SQL statement. Here’s an example of the SQL statement call that uses everything developed to this point:
SELECT column_value AS "File Names" FROM TABLE(list_files(get_directory_path('UPLOAD_FILES'))); |
It should return the item_import.csv physical file as the only file in the physical directory, like:
File Names ----------------- item_import.csv |
Mapping an External Table to a source File
The next step leverages the user segment of the Oracle Database’s data catalog and all the components developed above to find and display the external table and external file. This query returns the results:
COLUMN TABLE_NAME FORMAT A30 COLUMN file_name FORMAT A30 SELECT xt.table_name , xt.file_name FROM (SELECT uxt.TABLE_NAME , ixt.column_value AS file_name FROM user_external_tables uxt CROSS JOIN TABLE(list_files(get_directory_path(uxt.default_directory_name))) ixt) xt JOIN user_external_locations xl ON xt.table_name = xl.table_name AND xt.file_name = xl.location; |
It should return the following:
TABLE_NAME FILE_NAME ------------------------------ ------------------------------ ITEM_IMPORT_EXT_TABLE item_import.csv |
You can migrate the query into the following function. It returns a zero when the file isn’t found and a one when it is found.
CREATE OR REPLACE FUNCTION external_file_found ( table_in VARCHAR2 ) RETURN NUMBER IS -- Define a default return value. retval NUMBER := 0; -- Decalre a cursor to find external tables. CURSOR c (cv_table VARCHAR2) IS SELECT xt.table_name , xt.file_name FROM (SELECT uxt.TABLE_NAME , ixt.column_value AS file_name FROM user_external_tables uxt CROSS JOIN TABLE(list_files(get_directory_path(uxt.default_directory_name))) ixt) xt JOIN user_external_locations xl ON xt.table_name = xl.table_name AND xt.file_name = xl.location AND xt.table_name = UPPER(cv_table); BEGIN FOR i IN c(table_in) LOOP retval := 1; END LOOP; RETURN retval; END; / |
With the EXTERNAL_FILE_FOUND function, you can create a function that returns rows when the external file is found and no rows when the external file isn’t found. The following view hides the logic required to make that work:
CREATE OR REPLACE VIEW item_import AS SELECT * FROM item_import_ext_table WHERE external_file_found('ITEM_IMPORT_EXT_TABLE') = 1; |
Conveniently, you can now query the ITEM_IMPORT view without the risk of raising the following error when the file is missing:
SELECT * FROM item_import_ext_table * ERROR at line 1: ORA-29913: error IN executing ODCIEXTTABLEOPEN callout ORA-29400: DATA cartridge error KUP-04040: file item_import.csv IN UPLOAD_FILES NOT found |
You can now grant the SELECT privilege on the ITEM_IMPORT view to your application schema, like:
GRANT SELECT ON item_import TO application; |
After granting the SELECT privilege on the ITEM_IMPORT view to the APPLICATION schema, you can create a synonym to hide the IMPORT schema.
CREATE SYNONYM item_import FOR item_import; |
At this point, many developers feel they’re done. Enclosing the results in a schema-level function provides more utility than a view. The next section shows you how to replace the view with a schema-level function.
Replacing the View with an Object Table Function
Inside a schema-level function, you can assign the results from the query to a SQL collection of an object type. The object type should mirror the structure of the table, like the following:
1 2 3 4 5 6 7 8 9 | CREATE OR REPLACE TYPE item_import_object IS OBJECT ( asin_number VARCHAR2(10) , item_type VARCHAR2(15) , item_title VARCHAR2(60) , item_subtitle VARCHAR2(60) , item_rating VARCHAR2(8) , item_rating_agency VARCHAR2(4) , item_release_date DATE); / |
After creating the object type that mirrors the structure of the ITEM_IMPORT_EXT_TABLE table, you need to create a list like collection of the object type. The nested table collection type acts like a list in Oracle:
1 2 3 | CREATE OR REPLACE TYPE item_import_object_table IS TABLE OF item_import_object; / |
After defining the object type and collection, you can access them in the following type of function:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 | CREATE OR REPLACE FUNCTION external_file_contents ( table_in VARCHAR2 ) RETURN item_import_object_table IS -- Define a local counter. lv_counter NUMBER := 1; -- Construct an empty collection of ITEM_IMPORT_OBJECT data types. lv_item_import_table ITEM_IMPORT_OBJECT_TABLE := item_import_object_table(); -- Decalre a cursor to find external tables. CURSOR c (cv_table VARCHAR2) IS SELECT * FROM item_import_ext_table WHERE external_file_found(cv_table) = 1; BEGIN FOR i IN c(table_in) LOOP lv_item_import_table.EXTEND; lv_item_import_table(lv_counter) := item_import_object(i.asin_number ,i.item_type ,i.item_title ,i.item_subtitle ,i.item_rating ,i.item_rating_agency ,i.item_release_date); lv_counter := lv_counter + 1; END LOOP; /* * This is where you can place autonomous function calls: * ====================================================== * - These can read source and log files, and write them * to CLOB attributes for later inspection or review. * - These can call Java libraries to delete files, but * you should note that Java deletes any file rather * than moving it to the trash bin (where you might * recover it. */ RETURN lv_item_import_table; END; / |
Between the assignment to the collection and the return statement of the function, you have the ability of calling any number of autonomous functions. Any schema-level function can call autonomous functions that read and write tables with DML statements, like the INSERT, UPDATE, and DELETE statements. You can also call schema-functions that wrap Java libraries that delete external files.
You can confirm that the steps work by running the following query with or without the SQL*Plus formatting:
/* * SQL*Plus formatting. */ SET PAGESIZE 99 COLUMN asin_number FORMAT A11 HEADING "ASIN #" COLUMN item_title FORMAT A46 HEADING "ITEM TITLE" COLUMN item_rating FORMAT A6 HEADING "RATING" COLUMN item_release_date FORMAT A11 HEADING "RELEASE|DATE" /* * Query works only when item_import.csv file is present. */ SELECT asin_number , item_title , item_rating , TO_CHAR(item_release_date,'DD-MON-YYYY') AS item_release_date FROM TABLE(external_file_contents('ITEM_IMPORT_EXT_TABLE')); |
It should return the following from SQL*Plus:
RELEASE ASIN # ITEM TITLE RATING DATE ----------- ---------------------------------------------- ------ ----------- B000W74EQC Harry Potter and the Sorcerer's Stone PG 11-DEC-2007 B000W746GK Harry Potter and the Chamber of Secrets PG 11-DEC-2007 B000W796OM Harry Potter and the Prisoner of Azkaban PG 11-DEC-2007 B000E6EK2Y Harry Potter and the Goblet of Fire PG-13 07-MAR-2006 B000W7F5SS Harry Potter and the Order of the Phoenix PG-13 11-DEC-2007 B002PMV9FG Harry Potter and the Half-Blood Prince PG 08-DEC-2009 B001UV4XHY Harry Potter and the Deathly Hallows, Part 1 PG-13 15-APR-2011 B001UV4XIS Harry Potter and the Deathly Hallows, Part 2 PG-13 11-NOV-2011 |
The creation of the schema-level function lets you recreate the ITEM_IMPORT view. The following view would encapsulate (or hide) the presence of the function, which hides all the infrastructure components developed before this section (see line 14 in the function):
1 2 3 | CREATE OR REPLACE VIEW item_import AS SELECT * FROM TABLE(external_file_contents('ITEM_IMPORT_EXT_TABLE')); |
Implementing a Managed Import Process
During any import the information from the import process is exposed and one or more items may fail during the import process. That means the source file and loading log files must be preserved immediately after reading the data successfully. This is done by loading the data source file and log, discard, and bad import files into database tables. Only the source and log files exist when all rows are well formed, but the log files are reused for any subsequent load and require human inspection to isolate a specific upload.
The best way to implement this requires creating individual tables to hold each of the four potential large objects. The ITEM_MASTER table holds a transactional primary key and a table name for the import table. The primary key of the ITEM_MASTER table is the base key for imports and the ITEM_DATA, ITEM_LOG, ITEM_DISCARD, and ITEM_BAD tables hold foreign keys that point back to the ITEM_MASTER table’s primary key. These tables also hold a character large object column (CLOB), which will hold the respective source data file or log, discard, or bad files.
The following create the tables for the logging framework:
CREATE TABLE import_master ( import_master_id NUMBER CONSTRAINT pk_import_master PRIMARY KEY , import_table VARCHAR2(30)); -- Create sequence for import master. CREATE SEQUENCE import_master_s; -- Create import table. CREATE TABLE import_data ( import_data_id NUMBER CONSTRAINT pk_import_data PRIMARY KEY , import_master_id NUMBER , import_data CLOB , CONSTRAINT fk_import_data FOREIGN KEY (import_data_id) REFERENCES import_master (import_master_id)) LOB (import_data) STORE AS BASICFILE item_import_clob (TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768 PCTVERSION 10 NOCACHE LOGGING STORAGE (INITIAL 1048576 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645)); -- Create sequence for import master. CREATE SEQUENCE import_data_s; -- Create import table. CREATE TABLE import_log ( import_log_id NUMBER CONSTRAINT pk_import_log PRIMARY KEY , import_master_id NUMBER , import_log CLOB , CONSTRAINT fk_import_log FOREIGN KEY (import_log_id) REFERENCES import_master (import_master_id)) LOB (import_log) STORE AS BASICFILE item_import_log_clob (TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768 PCTVERSION 10 NOCACHE LOGGING STORAGE (INITIAL 1048576 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645)); -- Create sequence for import master. CREATE SEQUENCE import_log_s; -- Create import table. CREATE TABLE import_discard ( import_discard_id NUMBER CONSTRAINT pk_import_discard PRIMARY KEY , import_master_id NUMBER , import_discard CLOB , CONSTRAINT fk_import_discard FOREIGN KEY (import_discard_id) REFERENCES import_master (import_master_id)) LOB (import_discard) STORE AS BASICFILE item_import_discard_clob (TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768 PCTVERSION 10 NOCACHE LOGGING STORAGE (INITIAL 1048576 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645)); -- Create sequence for import master. CREATE SEQUENCE import_discard_s; -- Create import table. CREATE TABLE import_bad ( import_bad_id NUMBER CONSTRAINT pk_import_bad PRIMARY KEY , import_master_id NUMBER , import_bad CLOB , CONSTRAINT fk_import_bad FOREIGN KEY (import_bad_id) REFERENCES import_master (import_master_id)) LOB (import_bad) STORE AS BASICFILE item_import_bad_clob (TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768 PCTVERSION 10 NOCACHE LOGGING STORAGE (INITIAL 1048576 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645)); -- Create sequence for import master. CREATE SEQUENCE import_bad_s; |
The tables set the targets for uploading the source and log files. You should note that the table name is also the column name for the CLOB column, this becomes convenient when supporting a Native Dynamic SQL (NDS) statement in a single autonomous function. The LOAD_CLOB_FROM_FILE function supports reading the external source and log files and writing them their respective tables.
There is a DEADLOCK possibility with this type of architecture. It requires that the base row in the IMPORT_MASTER table is committed before attempting inserts into one of the dependent tables. A call to the function raises an error when the primary key column hasn’t been committed before hand.
You already set the access privileges for the DBMS_LOB package when you granted them to the UPLOAD_FILES and UPLOAD_LOGS virtual directories. This function only requires read permissions, which were granted to both virtual directories.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 | CREATE OR REPLACE FUNCTION load_clob_from_file ( pv_src_file_name IN VARCHAR2 , pv_virtual_dir IN VARCHAR2 , pv_table_name IN VARCHAR2 , pv_column_name IN VARCHAR2 , pv_foreign_key IN NUMBER ) RETURN NUMBER IS -- Declare placeholder for sequence generated primary key. lv_primary_key NUMBER; -- Declare default return value. lv_retval NUMBER := 0; -- Declare local variables for DBMS_LOB.LOADCLOBFROMFILE procedure. des_clob CLOB; src_clob BFILE := BFILENAME(pv_virtual_dir,pv_src_file_name); des_offset NUMBER := 1; src_offset NUMBER := 1; ctx_lang NUMBER := dbms_lob.default_lang_ctx; warning NUMBER; -- Declare pre-reading size. src_clob_size NUMBER; -- Declare variables for handling NDS sequence value. lv_sequence VARCHAR2(30); lv_sequence_output NUMBER; lv_sequence_tagline VARCHAR2(10) := '_s.nextval'; -- Define local variable for Native Dynamic SQL (NDS) Statement. stmt VARCHAR2(2000); -- Declare the function as an autonomous transaction. PRAGMA AUTONOMOUS_TRANSACTION; BEGIN -- Open file only when found. IF dbms_lob.fileexists(src_clob) = 1 AND NOT dbms_lob.isopen(src_clob) = 1 THEN src_clob_size := dbms_lob.getlength(src_clob); dbms_lob.open(src_clob,dbms_lob.lob_readonly); END IF; -- Concatenate the sequence name with the tagline. lv_sequence := pv_table_name || lv_sequence_tagline; -- Assign the sequence through an anonymous block. stmt := 'BEGIN ' || ' :output := '||lv_sequence||';' || 'END;'; -- Run the statement to extract a sequence value through NDS. EXECUTE IMMEDIATE stmt USING IN OUT lv_sequence_output; -- Create a dynamic statement that works for all source and log files. -- ---------------------------------------------------------------------- -- NOTE: This statement requires that the row holding the primary key -- has been committed because otherwise it raises the following -- error because it can't verify the integrity of the foreign -- key constraint. -- ---------------------------------------------------------------------- -- DECLARE -- * -- ERROR at line 1: -- ORA-00060: deadlock detected while waiting for resource -- ORA-06512: at "IMPORT.LOAD_CLOB_FROM_FILE", line 50 -- ORA-06512: at line 20 -- ---------------------------------------------------------------------- stmt := 'INSERT INTO '||pv_table_name||' '||CHR(10)|| 'VALUES '||CHR(10)|| '('||lv_sequence_output||CHR(10)|| ','||pv_foreign_key||CHR(10)|| ', empty_clob())'||CHR(10)|| 'RETURNING '||pv_column_name||' INTO :locator'; -- Run dynamic statement. EXECUTE IMMEDIATE stmt USING OUT des_clob; -- Read and write file to CLOB, close source file and commit. dbms_lob.loadclobfromfile( dest_lob => des_clob , src_bfile => src_clob , amount => dbms_lob.getlength(src_clob) , dest_offset => des_offset , src_offset => src_offset , bfile_csid => dbms_lob.default_csid , lang_context => ctx_lang , warning => warning ); -- Close open source file. dbms_lob.close(src_clob); -- Commit write and conditionally acknowledge it. IF src_clob_size = dbms_lob.getlength(des_clob) THEN COMMIT; lv_retval := 1; ELSE RAISE dbms_lob.operation_failed; END IF; RETURN lv_retval; END load_clob_from_file; / |
You can test this procedure against the data source file with the following script file:
-- Insert a sample row in the master table. INSERT INTO import_master VALUES (import_master_s.nextval,'ITEM_IMPORT_EXT_TABLE'); -- Record the row value to avoid deadlock on uncommitted master record. COMMIT; -- Test program for loading CLOB files. DECLARE -- Declare testing variables. lv_file_name VARCHAR2(255) := 'item_import.csv'; lv_virtual_dir VARCHAR2(255) := 'UPLOAD_FILES'; lv_table_name VARCHAR2(30) := 'IMPORT_DATA'; lv_column_name VARCHAR2(30) := 'IMPORT_DATA'; lv_foreign_key NUMBER; BEGIN -- Assign the current value of the sequence to a local variable. lv_foreign_key := import_master_s.currval; -- Check if you can read and insert a CLOB column. IF load_clob_from_file(lv_file_name ,lv_virtual_dir ,lv_table_name ,lv_table_name ,lv_foreign_key) = 1 THEN -- Display a successful subordinate routine. dbms_output.put_line('Subordinate routine succeeds.'); ELSE -- Display a failed subordinate routine. dbms_output.put_line('Subordinate routine fails.'); END IF; END load_clob_from_file; / |
You can test this procedure against the log file with the following script file:
DECLARE -- Declare testing variables. lv_file_name VARCHAR2(255) := 'item_import_ext_table.log'; lv_virtual_dir VARCHAR2(255) := 'UPLOAD_LOGS'; lv_table_name VARCHAR2(30) := 'IMPORT_LOG'; lv_column_name VARCHAR2(30) := 'IMPORT_LOG'; lv_foreign_key NUMBER; BEGIN -- Assign the current value of the sequence to a local variable. lv_foreign_key := import_master_s.currval; dbms_output.put_line('Foreign key ['||lv_foreign_key||']'); -- Check if you can read and insert a CLOB column. IF load_clob_from_file(lv_file_name ,lv_virtual_dir ,lv_table_name ,lv_table_name ,lv_foreign_key) = 1 THEN -- Display a successful subordinate routine. dbms_output.put_line('Subordinate routine succeeds.'); ELSE -- Display a failed subordinate routine. dbms_output.put_line('Subordinate routine fails.'); END IF; END; / |
You now have the ability to read and store the source and log files in CLOB columns. The next step is to write a master function that writes the master row and calls the LOAD_CLOB_FROM_FILE function for the source file and each of the log files. That’s what the CLEANUP_EXTERNAL_FILES function provides.
Unfortunately, the Java logic requires using the logical and operation, which is two ampersands (&&). This requires that you turn off substitution variables in SQL*Plus. You do that by disabling DEFINE, like this:
SET DEFINE OFF |
You can compile this Java library file after you’ve disabled LOAD_CLOB_FROM_FILE:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 | CREATE OR REPLACE FUNCTION cleanup_external_files ( table_in VARCHAR2 , data_directory_in VARCHAR2 , log_directory_in VARCHAR2 ) RETURN NUMBER IS -- Declare a local Attribute Data Type (ADT). TYPE list IS TABLE OF VARCHAR2(3); -- Declare a collection. lv_extension LIST := list('csv','log','bad','dis'); -- Define a default return value. retval NUMBER := 0; -- Declare base target table name. lv_target_table VARCHAR2(30) := 'IMPORT'; lv_foreign_key NUMBER; -- Decalre a cursor to find external tables. CURSOR check_source (cv_table_name VARCHAR2) IS SELECT xt.file_name FROM (SELECT uxt.TABLE_NAME , ixt.column_value AS file_name FROM user_external_tables uxt CROSS JOIN TABLE(list_files(get_directory_path(uxt.default_directory_name))) ixt) xt JOIN user_external_locations xl ON xt.TABLE_NAME = xl.TABLE_NAME AND xt.file_name = xl.location AND xt.TABLE_NAME = UPPER(cv_table_name); -- Declare a cursor to find files and compare for one input file name. CURSOR check_logs (cv_file_name VARCHAR2) IS SELECT list.column_value FROM TABLE(list_files(get_directory_path('UPLOAD_LOGS'))) list JOIN (SELECT cv_file_name AS file_name FROM dual) FILTER ON list.column_value = FILTER.file_name; -- Declare the function as autonomous. PRAGMA AUTONOMOUS_TRANSACTION; BEGIN -- Master loop to check for source and log files. FOR i IN check_source (table_in) LOOP -- Assign next sequence value to local variable. lv_foreign_key := import_master_s.nextval; -- Write the master record and commit it for the autonomous threads. INSERT INTO import_master VALUES (lv_foreign_key,'ITEM_IMPORT_EXT_TABLE'); COMMIT; -- Process all file extensions. FOR j IN 1..lv_extension.COUNT LOOP -- The source data file is confirmed by the CHECK_SOURCE cursor. IF lv_extension(j) = 'csv' THEN -- Load the source data file. -- ---------------------------------------------------------- -- The RETVAL holds success or failure, this approach -- suppresses an error when the file can't be loaded. -- It should only occur when there's no space available -- in the target table. retval := load_clob_from_file(i.file_name ,data_directory_in ,lv_target_table||'_DATA' ,lv_target_table||'_DATA' ,lv_foreign_key); lv_foreign_key := lv_foreign_key + 1; ELSE -- Verify that log file exists before attempting to load it. FOR k IN check_logs (LOWER(table_in)||'.'||lv_extension(j)) LOOP -- Load the log, bad, or dis(card) file. -- ---------------------------------------------------------- -- The RETVAL holds success or failure, as mentioned above. retval := load_clob_from_file(LOWER(table_in)||'.'||lv_extension(j) ,log_directory_in ,lv_target_table||'_'||lv_extension(j) ,lv_target_table||'_'||lv_extension(j) ,lv_foreign_key); END LOOP; END IF; END LOOP; retval := 1; END LOOP; RETURN retval; END; / |
Deleting Files from Virtual Directories
After you’ve read the files through a query and uploaded the source and log files to the database, you need to cleanup the files. This can be done by using another Java library function, provided you granted read, write, and delete privileges to the internal Java permissions file.
The DeleteFile Java library deletes files from the file system. It doesn’t put them in the trash can for final delete, it removes them completely.
Now you can build the Java library that lets you delete a file. A quick caveat, this code includes an AND logical operator that is two ampersands (&&). SQL uses an ampersand (&) for substitution variables. You’ll need to suppress that behavior when you run this code.
You do that by issuing the following command to disable substitution variables in SQL*Plus:
1 | SET DEFINE OFF |
You create the DeleteFile library like this:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | CREATE OR REPLACE AND COMPILE JAVA SOURCE NAMED "DeleteFile" AS // Java import statements import java.io.File; import java.security.AccessControlException; // Class definition. public class DeleteFile { // Define variable(s). private static File file; // Define copyTextFile() method. public static void deleteFile(String fileName) throws AccessControlException { // CREATE files FROM canonical file names. file = NEW File(fileName); // DELETE file(s). IF (file.isFile() && file.delete()) {}}} / |
You need a PL/SQL Wrapper to call the library, and here it is:
1 2 3 4 | CREATE OR REPLACE PROCEDURE delete_file (dfile VARCHAR2) IS LANGUAGE JAVA NAME 'DeleteFile.deleteFile(java.lang.String)'; / |
You can call this separately or embed it inside the UPLOAD_LOGS function, which saves re-writing the logic to find any source or log files.
This has provided you with an external table import framework. You can extend the framework by wrapping the query in an object table function. Such a function would afford you the opportunity to cleanup the source and log files after the query operation.
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