Question

So, I have the following: "SELECT * FROM MyTable;"

When I do the following I get the TableData back, which is useful, but still leaves some things unknown?

//CommandBehavior.KeyInfo seems to actually return the correct primary keys
// not so much with CommandBehavior.SchemaOnly.
IDataReader reader = command.ExecuteReader(CommandBehavior.KeyInfo)

DataTable table = reader.GetSchemaTable();

now, when iterating over my table I come across a column named “DataType” and it is either System.String or System.Byte[] or System.Int32, etc. But, this only tells me the .NET type to store, it doesn’t tell me if, for example, a System.Decimal is the DbType.Currency or DbType.Decimal. So when I’m creating an IDataParameter, I’m not sure what to set for the DbType.

parameter.ColumnName = columnName;
parameter.DbType = DbType.Decimal; (or should it have been Currency?)

Basically, how can I get the table’s real schema… or does it even matter?

Answer 1

If you are passing in parameters for a stored procedure, or some sql text, no you do not need to specify the parameters data type. the SqlCommand will correctly assign the data type for you.

I believe the ability to assign the DBType on a parameter is if you want to overwrite what the system would choose for you.

use the

SqlCommand.Parameters.AddWithValue("@parameterName", valueAsObject);

command

edit you are using the IDbCommand, not the SqlCommand. I know that both SqlCommand and Oracle command do not need you to specify the DbType, but I do not know if other frameworks do need you to explicitly set the DbType. here is a method to tranform a system.type to a DbType enum value:

Class DBTypeConversion
{
    private static String[,] DBTypeConversionKey = new String[,] 
    {
     {"BigInt","System.Int64"},
     {"Binary","System.Byte[]"},
     {"Bit","System.Boolean"},
     {"Char","System.String"},
     {"DateTime","System.DateTime"},
     {"Decimal","System.Decimal"},
     {"Float","System.Double"},
     {"Image","System.Byte[]"},
     {"Int","System.Int32"},
     {"Money","System.Decimal"},
     {"NChar","System.String"},
     {"NText","System.String"},
     {"NVarChar","System.String"},
     {"Real","System.Single"},
     {"SmallDateTime","System.DateTime"},
     {"SmallInt","System.Int16"},
     {"SmallMoney","System.Decimal"},
     {"Text","System.String"},
     {"Timestamp","System.DateTime"},
     {"TinyInt","System.Byte"},
     {"UniqueIdentifer","System.Guid"},
     {"VarBinary","System.Byte[]"},
     {"VarChar","System.String"},
     {"Variant","System.Object"}
    };


    public static SqlDbType SystemTypeToDbType( System.Type sourceType )
    {
    SqlDbType result;
    String SystemType = sourceType.ToString();
    String DBType = String.Empty;
    int keyCount = DBTypeConversionKey.GetLength(0);

    for(int i=0;i<keyCount;i++)
    {
    if(DBTypeConversionKey[i,1].Equals(SystemType)) DBType = DBTypeConversionKey[i,0];
    }

    if (DBType==String.Empty) DBType = "Variant";

    result = (SqlDbType)Enum.Parse(typeof(SqlDbType), DBType);

    return result;
    }

    public static Type DbTypeToSystemType( SqlDbType sourceType )
    {
    Type result;
    String SystemType = String.Empty;
    String DBType = sourceType.ToString();
    int keyCount = DBTypeConversionKey.GetLength(0);

    for(int i=0;i<keyCount;i++)
    {
    if(DBTypeConversionKey[i,0].Equals(DBType)) SystemType = DBTypeConversionKey[i,1];
    }

    if (SystemType==String.Empty) SystemType = "System.Object";

    result = Type.GetType(SystemType);

    return result;
    }

http://social.msdn.microsoft.com/Forums/en/winforms/thread/c6f3ab91-2198-402a-9a18-66ce442333a6
hope this helps better clarify.

http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlparametercollection.addwithvalue.aspx