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Api.JetEnumerateColumns method

  • Article

Efficiently retrieves a set of columns and their values from the current record of a cursor or the copy buffer of that cursor. The columns and values retrieved can be restricted by a list of column IDs, itagSequence numbers, and other characteristics. This column retrieval API is unique in that it returns information in dynamically allocated memory that is obtained using a user-provided realloc compatible callback. This new flexibility permits the efficient retrieval of column data with specific characteristics (such as size and multiplicity) that are unknown to the caller. This eliminates the need for the use of the discovery modes of JetRetrieveColumn to determine those characteristics in order to setup a final call to JetRetrieveColumn that will successfully retrieve the desired data.

This API is not CLS-compliant. 

Namespace:  Microsoft.Isam.Esent.Interop
Assembly:  Microsoft.Isam.Esent.Interop (in Microsoft.Isam.Esent.Interop.dll)

Syntax

'Declaration
<CLSCompliantAttribute(False)> _
Public Shared Function JetEnumerateColumns ( _
    sesid As JET_SESID, _
    tableid As JET_TABLEID, _
    numColumnids As Integer, _
    columnids As JET_ENUMCOLUMNID(), _
    <OutAttribute> ByRef numColumnValues As Integer, _
    <OutAttribute> ByRef columnValues As JET_ENUMCOLUMN(), _
    allocator As JET_PFNREALLOC, _
    allocatorContext As IntPtr, _
    maxDataSize As Integer, _
    grbit As EnumerateColumnsGrbit _
) As JET_wrn
'Usage
Dim sesid As JET_SESID
Dim tableid As JET_TABLEID
Dim numColumnids As Integer
Dim columnids As JET_ENUMCOLUMNID()
Dim numColumnValues As Integer
Dim columnValues As JET_ENUMCOLUMN()
Dim allocator As JET_PFNREALLOC
Dim allocatorContext As IntPtr
Dim maxDataSize As Integer
Dim grbit As EnumerateColumnsGrbit
Dim returnValue As JET_wrn

returnValue = Api.JetEnumerateColumns(sesid, _
    tableid, numColumnids, columnids, _
    numColumnValues, columnValues, allocator, _
    allocatorContext, maxDataSize, grbit)

[CLSCompliantAttribute(false)]
public static JET_wrn JetEnumerateColumns(
    JET_SESID sesid,
    JET_TABLEID tableid,
    int numColumnids,
    JET_ENUMCOLUMNID[] columnids,
    out int numColumnValues,
    out JET_ENUMCOLUMN[] columnValues,
    JET_PFNREALLOC allocator,
    IntPtr allocatorContext,
    int maxDataSize,
    EnumerateColumnsGrbit grbit
)

Parameters

  • numColumnids
    Type: System.Int32

    The numbers of JET_ENUMCOLUMNIDS.

  • columnids
    Type: []

    An optional array of column IDs, each with an optional array of itagSequence numbers to enumerate.

  • numColumnValues
    Type: System.Int32

    Returns the number of column values retrieved.

  • columnValues
    Type: []

    Returns the enumerated column values.

  • allocatorContext
    Type: System.IntPtr

    Context for the allocation callback.

  • maxDataSize
    Type: System.Int32

    Sets a cap on the amount of data to return from a long text or long binary column. This parameter can be used to prevent the enumeration of an extremely large column value.

Return value

Type: Microsoft.Isam.Esent.Interop.JET_wrn
A warning or success.

See also

Reference

Api class

Api members

Microsoft.Isam.Esent.Interop namespace