Selecting the LO Handle

The SELECT statement can select an LO handle of a smart large object from a CLOB, BLOB, or opaque-type column. Because the desired result of a query is usually the contents of an object, not just its LO handle, the DataBlade API module must then use the LO handle that the mi_value( ) or mi_value_by_name( ) function returns to access the smart-large-object data in its sbspace.

To select a smart large object from the database

Execute the SELECT statement with a DataBlade API statement-execution function such as mi_exec( ) or mi_exec_prepared_statement( ).
Obtain the column value that the mi_value( ) or mi_value_by_name( ) function passes back in the MI_DATUM structure as appropriate for the control mode of the query:
- For binary representation, the MI_DATUM structure contains a pointer to an LO handle.
- For text representation, the MI_DATUM structure contains the hexadecimal dump of an LO handle. To access the smart-large-object data, you must convert the LO handle to its binary representation with mi_lo_from_string( ).
For more information, see Binary and Text Representations of an LO Handle.
Optionally, ensure that the LO handle is valid with mi_lo_validate( ).

Validating an LO Handle

An LO handle is valid when it correctly identifies the location of a smart large object in an sbspace. An LO handle might be invalid for either of the following reasons:

Use the mi_lo_validate( ) function to check whether an LO handle is valid. If mi_lo_validate( ) returns a positive integer, the LO handle is invalid. You can mark this LO handle as invalid with the mi_lo_invalidate( ) function. The following code fragment checks whether the LO handle that LO_hdl references is valid:

You can use the mi_lo_validate( ) function in the support function of an opaque data type that contains smart large objects. In the lohandles( ) support function, this function can determine unambiguously which LO handles are valid for the given instance of the opaque type.