Rick Rick - 1 month ago 13
C# Question

How to get DefaultValue of column from database schema in C#?

I'm trying to read information from my database schema in C# (.NET 4.5, SQL Server 2014). I was having trouble with some fields such as MaxLength/ColumnLength until I found a forum that mentioned setting the

DataAdapter.MissingSchemaAction
to
MissingSchemaAction.AddWithKey
. Unfortunately the DefaultValue field is still blank even for columns that have a default set in the "Default Value or Binding" in the Column Properties in SQL Server.

SqlDataAdapter dbadapter = new SqlDataAdapter(SELECT_STRING, CONN_STRING);
dbadapter.MissingSchemaAction = MissingSchemaAction.AddWithKey;
DataTable tbl = new DataTable();
dbadapter.Fill(tbl);

// I actually looped through all rows/columns, but the net effect here is...
tbl.Columns[0].DefaultValue; // blank for all columns

// Also tried accessing the schema table available through DataReader
IDataReader reader = tbl.CreateDataReader();
DataTable schemaTbl = reader.GetSchemaTable();
/*
* There are different schema fields here than in DataColumn,
* but DefaultValue still blank. I looped through them all but...
*/
schemaTbl.Rows[0]["DefaultValue"]; // blank for all columns


How can I read the default value from a column in my table using .NET (preferably without resorting to querying SQL's
sys.*
tables).

Clarification

When creating or altering a table, you can set a default value of a column if none is provided. I'm trying to get the default value.

Example:

CREATE TABLE Person
(
Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255) NOT NULL,
HomeState varchar(2) DEFAULT 'NY'
)


Now if I say,
INSERT INTO Person (Id, LastName, FirstName) VALUES (1, 'Doe', 'John')
the HomeState will be 'NY' even though I didn't set it.

Answer

Try using the Microsoft.SqlServer.Smo library as below:

using (var connection = new SqlConnection("connectionString"))
{
    var serverConnection = new ServerConnection(connection);
    var server = new Server(serverConnection);
    var database = server.Databases["databaseName"];
    var table = database.Tables["tableName"];

    foreach (Column column in table.Columns)
    {
        Console.WriteLine($"{column.Name} - default constraint: {column.DefaultConstraint?.Text ?? "None"}");
    }
    Console.ReadLine();
}