How to create array DbParameter[]

Question

The manual says that the ExecuteScalar method should be used like:

public T ExecuteScalar<T>( 
   string commandText,
   CommandType commandType,
   params DbParameter[] parameters
)

But how do I create that array of parameters? I need to provide my stored procedure 2 parameters.

Answer 1

• DbParameter is an abstract class.
• Since the type T can not be inferred from the usage, you have to specify it.

• Althought you can just pass a variable number of parameters without creating the array, if you are dynamically creating a variable number of parameters, the array is your friend.

  var parameters = new[]{
              new SqlParameter(){ ParameterName="foo", Value="hello" },
              new SqlParameter(){ ParameterName="bar", Value="World" }
          };
  x.ExecuteScalar<int>(commandText, commandType, parameters);
  

Answer 2

The parameters parameter has the params keyword. This means that you don't have to create the array explicitly but can pass a variable number of arguments to the method:

x.ExecuteScalar(commandText, commandType, parameter1, parameter2);

However, if you want, you can create the array explictly and pass it to the method as follows:

DbParameter[] parameters = new DbParameter[] { parameter1, parameter2 };

x.ExecuteScalar(commandText, commandType, parameters);

Answer 3

DbParameter is an abstract class - but you can instantiate the derived type.

If you are using Sql server it is SqlParameter:

 DbParameter[] parameters = new DbParameter[2]; 
 parameters[0]  = new SqlParameter("param1",  123456);
 parameters[1]  = new SqlParameter("param2",  "abcdef");

Answer 4

The params keyword means that you can specify a varying number of parameters (so from 1 to [pretty much] infinity).

You can just call the method like this: ExecuteScalar<SomeType>("Command!", CommandType.SomeCommandType, dbParameter1, dbParameter2);

Answer 5

In a "perfect world" you should create any single parameter by this code:

DbProviderFactory f = DbProviderFactories.GetFactory("System.Data.SqlClient");
DbParameter parameter = f.CreateParameter();

but you probably have to use some specific platform functionality that SqlParameter implements... as SqlCommand does: SqlCommand.Parameters.AddWithValue() etc.