Dynamic where clause in parameter

Question

I am currently trying to build up the where clause of an SqlCommand.

something similar to this

myCommand.CommandText = \"SELECT * \" +
          


        

Answer 1

It seems you're trying to add the entire WHERE clause as a parameter - that won't work!

So suppose you need to build something like this

SELECT * from TABLE1 WHERE Field1=@Field1Value and Field2=@Field2Value

And assuming

• you have a List<WhereField> of fields to include in the WHERE clause
• and that all clauses are ANDed together
• and WhereField looks something like this

---

public class WhereField
{
   public string FieldName{get;set;}
   public object FieldValue{get;set;}
   public string ComparisonOperator{get;set;}
}

then you have something like this:

var whereClause = new StringBuilder();
    foreach (var field in WhereFields)
    {
     whereClause.Append(field.FieldName)
     .Append(field.ComparisonOperator)
     .Append("@")
     .Append(field.FieldName).Append("Value")
     .Append (" AND ");
//add the parameter as well:
    myCommand.Parameters.AddWithValue("",field.FieldName+"Value");
    }
 //cleanly close the where clause
whereClause.Append("1=1");

And now you can execute

myCommand.CommandText = "SELECT * " +
                        "FROM TABLE1 WHERE " + whereClause.ToString();

Answer 2

May be you need

myCommand.CommandText = "SELECT * " +
                        "FROM TABLE1 WHERE " + 
                        "@whereClause";

Answer 3

You can't use a clause (where) with parameters, you are only allowed to use parameters with command.Parameters.

To build a dynamic Where clause, you have to build your query based on conditions and string concatenation and then add the parameters accordingly.

Something like:

sb.Append("SELECT * FROM TABLE1 ");

if (someCondition)
{
    sb.Append("WHERE XColumn = @XColumn");
    myCommand.Parameters.AddWithValue("@XColumn", "SomeValue");
}
else
{
    sb.Append("WHERE YColumn = @YColumn");
    myCommand.Parameters.AddWithValue("@YColumn", "SomeOtherValue");
}
myCommand.CommandText = sb.ToString();