Returning Output Parameters with Dapper for .NET Core

Question

I'm struggling with how to properly map output parameters back to an object using Dapper, when I create DynamicParamters from a template object.

var parameters = new DynamicParameters(entity);
parameters.Add("@Id", dbType: DbType.Int32, direction: ParameterDirection.Output);
parameters.Output(entity, x => x.Id);             

await conn.ExecuteAsync(
   "TodoItemInsert", entity, 
    commandType: CommandType.StoredProcedure);

My hope was that the above code would map the resulting ID back into the entity that I created the parameters from in the first place. No matter what I try I am unable to get the parameter to return from the stored procedure. Calling parameters.Get<int>("@Id") throws a KeyNotFoundException. parameters.Get<int?>("@Id") returns null.

My SQL is a very basic insert sproc

ALTER PROCEDURE [dbo].[TodoItemInsert]
    @Name VARCHAR(255)
    , @Description VARCHAR(512)
    , @DueDate DATETIME = NULL
    , @IsComplete BIT = 0
    , @Id INT OUTPUT 
AS

INSERT INTO
    [TodoItems]
(
    Name
    , Description
    , DueDate
    , IsComplete
)
VALUES
(
    @Name
    , @Description
    , @DueDate
    , @IsComplete
)

SET @Id = SCOPE_IDENTITY()

What is the correct way to get an output parameter back from Dapper when trying to use an object template for my DynamicParameters?

mclark1129 · Accepted Answer · 2016-08-09 13:18:54Z

12

Figured this out, didn't properly update my code when I moved from template to parameters. I was passing entity into my query, not parameters. Once I replaced that I could even get rid of the explicit addition of the Id output parameter. This is much nicer!

var parameters = new DynamicParameters(entity);
parameters.Output(entity, x => x.Id);             

await conn.ExecuteAsync(
   "TodoItemInsert", parameters, 
    commandType: CommandType.StoredProcedure);

answered Aug 9, 2016 at 13:18

mclark1129

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