c# - SqlBulkCopy into table that Default column values fails when source DataTable row has DBNull.Value

Question

Update: Here is my solution

I have a table defined as:

CREATE TABLE [dbo].[csvrf_References]
(
    [Ident] [int] IDENTITY(1,1) NOT NULL,
    [ReferenceID] [uniqueidentifier] NOT NULL DEFAULT (newsequentialid()),
    [Type] [nvarchar](255) NOT NULL,
    [Location] [nvarchar](1000) NULL,
    [Description] [nvarchar](2000) NULL,
    [CreatedOn] [datetime] NOT NULL DEFAULT (getdate()),
    [LastUpdatedOn] [datetime] NOT NULL DEFAULT (getdate()),
    [LastUpdatedUser] [nvarchar](100) NOT NULL DEFAULT (suser_sname()),

    CONSTRAINT [PK_References] PRIMARY KEY NONCLUSTERED ([ReferenceID] ASC)
) ON [PRIMARY]

I have a DataTable with columns that match the table column names and data types. The DataTable is filled out with DBNull.Value in CreatedOn, LastUpdatedOn and LastUpdatedUser. ReferenceID is already generated. When I call the following code I get the error below.

Code:

SqlBulkCopy bulkCopy = new SqlBulkCopy(conn, SqlBulkCopyOptions.Default, bulkCopyTran);
bulkCopy.DestinationTableName = table.TableName;
bulkCopy.ColumnMappings.Clear();
foreach (DataColumn col in table.Columns) bulkCopy.ColumnMappings.Add(col.ColumnName, col.ColumnName);
bulkCopy.WriteToServer(table);

Error:

Error trying to BulkCopy table csvrf_References
System.InvalidOperationException: Column 'CreatedOn' does not allow DBNull.Value.
at System.Data.SqlClient.SqlBulkCopy.ConvertValue(Object value, _SqlMetaData metadata, Boolean isNull, Boolean& isSqlType, Boolean& coercedToDataFeed)

I have looked all over and I can't seem to find an answer for this. The SqlBulkCopy class seems not to honor default values even though it says it does. What am I doing wrong here?

Answer 1

For part 1, "field that is NOT NULL with a DEFAULT", you should not be sending the field in the first place. It should not be mapped. There is no need to change that field to accept NULLs just for this.

For part 2, "field that is NULL with a DEFAULT", that will work to get the default value when passing in DbNull.Value, as long as you don't have the SqlBulkCopyOptions set to KeepNulls, else it will insert an actual database NULL.

Since there is some confusion about the SqlBulkCopyOption of KeepNulls, let's look at its definition:

Preserve null values in the destination table regardless of the settings for default values. When not specified, null values are replaced by default values where applicable.

This means that a DataColumn set to DbNull.Value will be inserted as a database NULL, even if the column has a DEFAULT CONSTRAINT, if the KeepNulls option is specified. It is not specified in your code. Which leads to the second part that says DbNull.Value values are replaced by "default values" where applicable. Here "applicable" means that the column has a DEFAULT CONSTRAINT defined on it. Hence, when a DEFAULT CONSTRAINT exists, a non-DbNull.Value value will be sent in as is while DbNull.Value should translate to the SQL keyword DEFAULT. This keyword is interpreted in an INSERT statement as taking the value of the DEFAULT constraint. Of course, it is also possible that SqlBulkCopy, if issuing individual INSERT statements, could simply leave that field out of the column list if set to NULL for that row, which would pick up the default value. In either case, the end result is that it works as you expected. And my testing shows that it does indeed work in this manner.

To be clear about the distinction:

• If a field in the database is set to NOT NULL and has a DEFAULT CONSTRAINT defined on it, your options are:

  • Pass in the field (i.e. it will not pick up the DEFAULT value), in which case it can never be set to DbNull.Value

  • Do not pass in the field at all (i.e. it will pick up the DEFAULT value), which can be accomplished by either:

    • Do not have it in the DataTable or query or DataReader or whatever is being sent in as the source, in which case you might not need to specify the ColumnMappings collection at all

    • If the field is in the source, then you must specify the ColumnMappings collection so that you can leave that field out of the mappings.

  • Setting, or not setting, KeepNulls does not change the above noted behavior.

• If a field in the database is set to NULL and has a DEFAULT CONSTRAINT defined on it, your options are:

  • Do not pass in the field at all (i.e. it will pick up the DEFAULT value), which can be accomplished by either:

    • Do not have it in the DataTable or query or DataReader or whatever is being sent in as the source, in which case you might not need to specify the ColumnMappings collection at all

    • If the field is in the source, then you must specify the ColumnMappings collection so that you can leave that field out of the mappings.

  • Pass in the field set to a value that is not DbNull.Value, in which case it will be set to this value and not pick up the DEFAULT value

  • Pass in the field as DbNull.Value, in which case the effect is determined by whether or not SqlBulkCopyOptions is being passed in and has been set to KeepNulls:

    • KeepNulls is not set will pick up the DEFAULT value

    • KeepNulls is set will leave the field set to NULL

---

Here is a simple test to see how the DEFAULT keyword works:

--DROP TABLE ##DefaultTest;
CREATE TABLE ##DefaultTest
(
  Col1 INT,
  [CreatedOn] [datetime] NOT NULL DEFAULT (GETDATE()),
  [LastUpdatedOn] [datetime] NULL DEFAULT (GETDATE())
);
INSERT INTO ##DefaultTest (Col1, CreatedOn) VALUES (1, DEFAULT);
INSERT INTO ##DefaultTest (Col1, LastUpdatedOn) VALUES (2, DEFAULT);
INSERT INTO ##DefaultTest (Col1, LastUpdatedOn) VALUES (3, NULL);
INSERT INTO ##DefaultTest (Col1, LastUpdatedOn) VALUES (4, '3333-11-22');

SELECT * FROM ##DefaultTest ORDER BY Col1 ASC;

Results:

Col1   CreatedOn                  LastUpdatedOn
1      2014-11-20 12:34:31.610    2014-11-20 12:34:31.610
2      2014-11-20 12:34:31.610    2014-11-20 12:34:31.610
3      2014-11-20 12:34:31.610    NULL
4      2014-11-20 12:34:31.613    3333-11-22 00:00:00.000