The object 'DF__*' is dependent on column '*' - Changing int to double

Question

Basically I got a table in my EF database with the following properties:

public int Id { get; set; }
public string Title { get; set; }
public string Descript         


        

Answer 1

I had this error trying to run a migration to work around it I renamed the column and re-generated the migration using

add-migration migrationname -force

in the package manager console. I was then able to run

update-database

successfully.

Answer 2

While dropping the columns from multiple tables, I faced following default constraints error. Similar issue appears if you need to change the datatype of column.

The object 'DF_TableName_ColumnName' is dependent on column 'ColumnName'.

To resolve this, I have to drop all those constraints first, by using following query

DECLARE @sql NVARCHAR(max)=''     
SELECT @SQL += 'Alter table ' + Quotename(tbl.name) + '  DROP constraint ' + Quotename(cons.name) + ';'
 FROM SYS.DEFAULT_CONSTRAINTS cons 
 JOIN   SYS.COLUMNS col ON col.default_object_id = cons.object_id
 JOIN   SYS.TABLES tbl ON tbl.object_id = col.object_id
 WHERE  col.[name] IN ('Column1','Column2')

--PRINT @sql
EXEC Sp_executesql @sql 

After that, I dropped all those columns (my requirement, not mentioned in this question)

DECLARE @sql NVARCHAR(max)='' 
SELECT @SQL += 'Alter table ' + Quotename(table_catalog)+ '.' + Quotename(table_schema) + '.'+ Quotename(TABLE_NAME) 
               + '  DROP column ' + Quotename(column_name) + ';'
FROM   information_schema.columns where COLUMN_NAME IN ('Column1','Column2')  
--PRINT @sql
EXEC Sp_executesql @sql 

I posted here in case someone find the same issue.

Happy Coding!

Answer 3

This is the tsql way

 ALTER TABLE yourtable DROP CONSTRAINT constraint_name     -- DF_Movies_Rating__48CFD27E

For completeness, this just shows @Joe Taras's comment as an answer

Answer 4

As constraint has unpredictable name, you can write special script(DropConstraint) to remove it without knowing it's name (was tested at EF 6.1.3):

public override void Up()
{    
    DropConstraint();
    AlterColumn("dbo.MyTable", "Rating", c => c.Double(nullable: false));
}

private void DropConstraint()
{
    Sql(@"DECLARE @var0 nvarchar(128)
          SELECT @var0 = name
          FROM sys.default_constraints
          WHERE parent_object_id = object_id(N'dbo.MyTable')
          AND col_name(parent_object_id, parent_column_id) = 'Rating';
          IF @var0 IS NOT NULL
              EXECUTE('ALTER TABLE [dbo].[MyTable] DROP CONSTRAINT [' + @var0 + ']')");
}

public override void Down()
{            
    AlterColumn("dbo.MyTable", "Rating", c => c.Int(nullable: false));    
}

Answer 5

I'm adding this as a response to explain where the constraint comes from. I tried to do it in the comments but it's hard to edit nicely there :-/

If you create (or alter) a table with a column that has default values it will create the constraint for you.

In your table for example it might be:

CREATE TABLE Movie (
    ...
    rating INT NOT NULL default 100
)

It will create the constraint for default 100.

If you instead create it like so

CREATE TABLE Movie (
  name VARCHAR(255) NOT NULL,
  rating INT NOT NULL CONSTRAINT rating_default DEFAULT 100
);

Then you get a nicely named constraint that's easier to reference when you are altering said table.

ALTER TABLE Movie DROP CONSTRAINT rating_default;
ALTER TABLE Movie ALTER COLUMN rating DECIMAL(2) NOT NULL;
-- sets up a new default constraint with easy to remember name
ALTER TABLE Movie ADD CONSTRAINT rating_default DEFAULT ((1.0)) FOR rating;

You can combine those last 2 statements so you alter the column and name the constraint in one line (you have to if it's an existing table anyways)

Answer 6

MS SQL Studio take care of when you delete the column but if you need to Delete Constraint Programmatically here is simple solution

Here’s a code snippet that’ll drop a column with a default constraint:

DECLARE @ConstraintName nvarchar(200)
SELECT @ConstraintName = Name FROM SYS.DEFAULT_CONSTRAINTS WHERE PARENT_OBJECT_ID = OBJECT_ID('__TableName__') AND PARENT_COLUMN_ID = (SELECT column_id FROM sys.columns WHERE NAME = N'__ColumnName__' AND object_id = OBJECT_ID(N'__TableName__'))
IF @ConstraintName IS NOT NULL
EXEC('ALTER TABLE __TableName__ DROP CONSTRAINT ' + @ConstraintName)
IF EXISTS (SELECT * FROM syscolumns WHERE id=object_id('__TableName__') AND name='__ColumnName__')
EXEC('ALTER TABLE __TableName__ DROP COLUMN __ColumnName__')

Just replace TableName and ColumnName with the appropriate values. You can safely run this even if the column has already been dropped.

Bonus: Here’s the code to drop foreign keys and other types of constraints.

IF EXISTS(SELECT 1 FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE where TABLE_NAME = '__TableName__' AND COLUMN_NAME = '__ColumnName__')
BEGIN
SELECT @ConstraintName = CONSTRAINT_NAME FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE where TABLE_NAME = '__TableName__' AND COLUMN_NAME = '__ColumnName__'
EXEC('ALTER TABLE __TableName__ DROP CONSTRAINT ' + @ConstraintName)
END

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