SqlParameter.SourceColumnNullMapping Property

Definition

Namespace:

Microsoft.Data.SqlClient

Assembly:

Microsoft.Data.SqlClient.dll

Package:

Microsoft.Data.SqlClient v5.2.0

Sets or gets a value which indicates whether the source column is nullable. This allows SqlCommandBuilder to correctly generate Update statements for nullable columns.

public:
 virtual property bool SourceColumnNullMapping { bool get(); void set(bool value); };

public override bool SourceColumnNullMapping { get; set; }

member this.SourceColumnNullMapping : bool with get, set

Public Overrides Property SourceColumnNullMapping As Boolean

Property Value

Boolean

true if the source column is nullable; false if it is not.

Remarks

SourceColumnNullMapping is used by the SqlCommandBuilder to correctly generate update commands when dealing with nullable columns. Generally, use of SourceColumnNullMapping is limited to developers inheriting from SqlCommandBuilder.

DbCommandBuilder uses this property to determine whether the source column is nullable, and sets this property to true if it is nullable, and false if it is not. When SqlCommandBuilder is generating its Update statement, it examines the SourceColumnNullMapping for each parameter. If the property is true, SqlCommandBuilder generates a WHERE clauses like the following (in this query expression, "FieldName" represents the name of the field):

((@IsNull_FieldName = 1 AND FieldName IS NULL) OR   
  (FieldName = @Original_FieldName))  

If SourceColumnNullMapping for the field is false, SqlCommandBuilder generates the following WHERE clause:

FieldName = @OriginalFieldName  

In addition, @IsNull_FieldName contains 1 if the source field contains null, and 0 if it does not. This mechanism allows for a performance optimization in SQL Server, and provides for common code that works across multiple providers.