Dapper & MS Access - Read works, Write doesn't

ado.net c# dapper ms-access oledb

Question

Let's start by getting this out of the way: I'm stuck using an MS Access DB and I can't change it.

This works fine:

using (OleDbConnection conn = ConnectionHelper.GetConnection())
{
  conn.Open();
  var results = conn.Query<string>(
    "select FirstName from Students where LastName = @lastName", 
    new { lastName= "Smith" }
  );
  conn.Close();
}

This works fine:

using (OleDbConnection conn = ConnectionHelper.GetConnection())
{
  OleDbCommand cmd = new OleDbCommand(
    "update Students set FirstName = @firstName, City = @city where LastName = @lastName", 
    conn
  );
  cmd.Parameters.AddWithValue("firstName", "John");
  cmd.Parameters.AddWithValue("city", "SomeCity");
  cmd.Parameters.AddWithValue("lastName", "Smith");

  conn.Open();
  var result = cmd.ExecuteNonQuery();
  conn.Close();
}

This doesn't... it executes without error but it sets the FirstName as "SomeCity" in the DB and the City as "John":

using (OleDbConnection conn = ConnectionHelper.GetConnection())
{
  conn.Open();
  var results = conn.Query<string>(
    "update Students set FirstName = @firstName, City = @city where LastName = @lastName", 
    new { firstName = "John", city = "SomeCity", lastName = "Smith" }
  );
  conn.Close();
}

Any ideas?

EDIT BELOW

Dapper works if I use DynamicParameters:

using (OleDbConnection conn = ConnectionHelper.GetConnection())
{
  DynamicParameters parameters = new DynamicParameters();
  parameters.Add("firstName", "John");
  parameters.Add("city", "SomeCity");
  parameters.Add("lastName", "Smith");

  conn.Open();
  var result = conn.Query<string>(
    "update Students set FirstName = @firstName, City = @city where LastName = @lastName",
    parameters
  );
  conn.Close();
}

Accepted Answer

After some digging, I was able to find a cause:

Below is CreateParamInfoGenerator delegate from dapper's SqlMapper:

    public static Action<IDbCommand, object> CreateParamInfoGenerator(Identity identity)
    {

        // code above here
        IEnumerable<PropertyInfo> props = type.GetProperties().OrderBy(p => p.Name); 

The props is your unanimous param which gets re-ordered by OrderBy(p => p.Name), which moves city upfront.

new { firstName = "John", city = "SomeCity", lastName = "Smith" }

Props is then being added to the IDbCommand Parameters where the order is important.

If I comment out OrderBy() clause, then everything works.

I also tested DynamicParameters and intentionally re-ordered the attributes to move city upfront:

        var parameters = new DynamicParameters();
        parameters.Add("city", "SomeCity");
        parameters.Add("firstName", "John");
        parameters.Add("lastName", "Smith");

        var result = dbConnection.Query<string>(
          "update Students set FirstName = @firstName, City = @city where LastName = @lastName",
          parameters
        );

The above did not work as well, so the order of attributes is the reason!

I guess you can modify your local copy of SqlMapper for now and remove OrderBy() and wait for an official verdict from Marc...

Hope this helps.


Popular Answer

I had a similar issue, what I did was to use parameter names like @param1, @param2 instead of @name,@id,@price so the order stays the same without having to modify SQLMapper.cs file.

Something like

public void Update(Movie movie)
{
  var sql = "UPDATE myDB.movies set title=@param1, genre=@param2 where ID=@param3";
  db.Execute(sql, new { param1 = movie.Title, param2 = movie.Genre, param3 = movie.ID });
}



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Licensed under: CC-BY-SA with attribution
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Is this KB legal? Yes, learn why