Invalid Cast Exception, Stored Procedure, LINQ TO SQL

Question

9 months later, the same problem shows up again. I've tried everything I can think of:

• I cast as varchar(max) on the stored procedure;
• I changed the mapping;
• tried to find the collection linq works with, but couldn't find anywhere;

I have been running this stored procedure for some time Mapping it to my objects using LINQ to SQL, and now, all of the sudden, LINQ is trying to cast the field 'value' as double.

---

the error:

specified cast is not valid    
   System.Data.SqlClient.SqlBuffer.get_Double()
   System.Data.SqlClient.SqlDataReader.GetDouble(Int32 i)
   Read_Field(ObjectMaterializer`1 )
   System.Data.Linq.SqlClient.ObjectReaderCompiler.ObjectReader`2.MoveNext()
   System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)
   CmsCsharp.BL.FieldManager.FindContentField(Int32 id_content, Int32 id_fieldType, String fieldName) 

---

the methods

public static Field FindContentField(int id_content, int id_fieldType, string fieldName)
            {
                using (DbBase conn = new DbBase())
                {
                    try
                    {
                        return conn.ClientDB.sprocFindContentField(id_content, id_fieldType, fieldName).Single();
                    }
                    catch (Exception e)
                    {
                        return null;
                    }
                }
            }



[Function(Name = "dbo.sprocFindContentField")]
        public ISingleResult<Field> sprocFindContentField([Parameter(DbType="Int")] System.Nullable<int> id_content, [Parameter(DbType="Int")]System.Nullable<int> id_fieldType, [Parameter(DbType="Varchar(255)")]string fieldName)
        {
            IExecuteResult result = this.ExecuteMethodCall(this, ((MethodInfo)(MethodInfo.GetCurrentMethod())), id_content, id_fieldType, fieldName);
            return ((ISingleResult<Field>)(result.ReturnValue));
        }

---

the field:

public class TextField : Field
{
   private string _Value;

    [Column(Storage="_Value", DbType="VarChar(MAX) NOT NULL", Name="value", CanBeNull=true)]
    public string Value
    { //get and set }
}

---

the procedure:

  SELECT 
         type = 'textField',
         fieldLabel.id_fieldEditor,
         fieldLabel.id_fieldType ,
         fieldLabel.description,
         fieldLabel.id ,         
         sessionField.id  AS relationId,
         fieldLabel.name ,
         fieldText.content AS value,
         fieldText.id  AS valueId,
         cf.id as contentRelationId
  FROM
         fieldLabel
  INNER JOIN
         sessionField
  ON
         sessionField.id_fieldLabel = fieldLabel.id
  INNER JOIN
        cms_contentField AS cf
  ON
        cf.id_sessionField = sessionField.id
  INNER JOIN
         fieldText
  ON
         fieldText.id = cf.id_fieldValue
  INNER JOIN
        fieldType
  ON
        fieldLabel.id_fieldType = fieldType.id
  INNER JOIN
        fieldTable
  ON
        fieldTable.id = fieldType.id_fieldTable
  WHERE
         cf.id_content = @id_content
  AND
        fieldTable.id = 1

Answer 1

My guess is that you have a value in your table that is triggering SQL Server's conversion through the "numeric" data type. i.e. your value is being converted into an imprecise data type (float or real) and causing LINQ to SQL to attempt a double. See the caution in SQL Server's help file for int

Answer 2

I've changed the 9th line in the stored procedure to fieldText.content,

SELECT 
     type = 'textField',
     fieldLabel.id_fieldEditor,
     fieldLabel.id_fieldType ,
     fieldLabel.description,
     fieldLabel.id ,         
     sessionField.id  AS relationId,
     fieldLabel.name ,
     fieldText.content AS value, //this line
     fieldText.id  AS valueId,
     cf.id as contentRelationId

then I changed the mapping accordingly:

[Column(Storage="_Value", DbType="VarChar(MAX) NOT NULL", Name="content", CanBeNull=true)]
public string Value
{ //get and set }

and it worked!

Have no idea why it worked. Does the labeling (as value) could be the cause?

Thank you