SELECT - LOB Handles
An LOB from the results 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 data source component; this 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.
- a reader 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_LOCATOR or 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 column of the result sets and
the static type of the target variable, or using the addition
CREATING 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
Accessing a closed LOB handle produces a runtime error.
Special properties of open reader streams and locators:
- As long as a reader stream for an ABAP 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 reader stream using
ENDSELECT. In this case, a reference to an object of the class CL_ABAP_SQL_SELECT_STATEMENT (a subclass of CL_ABAP_SQL_STATEMENT_HANDLE) can be obtained 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 ABAP 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 while a locator is open, an internal copy of the LOB data for the locator is created on the database first.
The following restrictions apply:
- A maximum of 16 data streams can be opened for an ABAP SQL statement.
- In a database LUW there can be a maximum of 16 ABAP SQL statements whose data streams are open at the same time.
- A maximum of 1000 LOB handles can be open in a database LUW.
- If LOB handles are created using the addition
SINGLE, all primary key fields in logical expressions joined using
WHEREcondition are checked for equality.
Always close a LOB handle as soon as possible using its method CLOSE. Also refer to Streaming and Locators.
Reads a BLOB to a reader stream.
DATA reader TYPE REF TO cl_abap_db_x_reader. SELECT SINGLE picture FROM demo_blob_table WHERE name = '...' INTO @reader.