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SELECT - LOB handles

In the statement SELECT , LOB handles can be created as reader streams and as locators.

Other versions: 7.31 | 7.40 | 7.54

Prerequisites

An LOB from the result set can be assigned to an LOB handle component of a work area, or to an individual reference variable for an LOB handle. The static type of all LOB handle components must contain the interface IF_ABAP_DB_LOB_HANDLE and match the corresponding database table component, that means they must be less specific or the same as one of the following system classes for streaming or locators:

  • CL_ABAP_DB_C_READER or CL_ABAP_DB_C_LOCATOR in the case of CLOBs.
  • CL_ABAP_DB_X_READER or CL_ABAP_DB_X_LOCATOR in the case of BLOBs.

The stream type or locator type must match the data type of the LOBs.

Rules

If an LOB from the result set of a selection is assigned to an LOB handle component of a work area or to an individual reference variable for an LOB handle, either

  • a read stream is created as an instance of one of the classes CL_ABAP_DB_C_READER, CL_ABAP_DB_X_READER or,
  • a locator is created as an instance of one of the classes CL_ABAP_DB_C_LOCATORor CL_ABAP_DB_X_LOCATOR

and after the execution of the SELECT statement the reference variable points to the object. The class used is determined using the data type of the result set column and the static type of the target variable, or using the CREATING addition if required. The LOB to be read can be evaluated or forwarded using LOB handle methods.

A LOB handle created in this way, that is a reader stream or a locator, exists until it:

  • is closed explicitly using its CLOSE method from the IF_ABAP_CLOSE_RESOURCE interface,
  • is closed implicitly at the end of the current database LUW.

Reader streams, but not locators, are also closed implicitly by the statement ENDSELECT .

Accessing a closed LOB handle leads to a runtime error.

Special properties of open reader streams and locators:

  • As long as a reader stream for an Open SQL statement is still open, the corresponding database is not closed. This can only occur with SELECT SINGLE, since there is no implicit termination of the read stream using ENDSELECT. In this case, you can get a reference to an object of the class CL_ABAP_SQL_SELECT_STATEMENT, a subclass of CL_ABAP_SQL_STATEMENT_HANDLE, from the interface IF_ABAP_DB_READER using the method GET_STATEMENT_HANDLE before closing the reader stream. The methods of the abstract superclass implemented there can be used to check the state of the Open SQL statement, and all streams that are still open can be closed.
  • It is guaranteed that, once created, a locator always works with the same LOB data. If the associated LOB column is modified whilst a locator is open, an internal copy of the LOB data for the locatoris created on the database first.

Restrictions

The following restrictions apply:

  • A maximum of 16 data streams can be opened for an Open SQL statement.
  • In a database LUW there can be a maximum of 16 Open SQL statements whose streams are open at the same time.
  • A maximum of 1000 LOB handles can be open in a database LUW.
  • If the creation of LOB handles takes place with the SINGLE addition, all primary key fields in logical expressions linked with AND in the WHERE condition are checked for equality.


Note

Always close a LOB handle as soon as possible using its method CLOSE. Also refer to Streaming and Locators.

Examples