Question

With the following code, I search for a specific Matrix in my repository and then assign it to Shuttle property.

var requestRepository = unitOfWork.Create<Request>();
var matrixRepository = unitOfWork.Create<Matrix>();
...
var matrix = matrixRepository.Find(m => m.MatrixID == matrixID).FirstOrDefault();
request.Shuttle = matrix;
....

This works. I try another alternative. With the following code, I prepare a Matrix object and try to attach it to my repository.

var requestRepository = unitOfWork.Create<Request>();
var matrixRepository = unitOfWork.Create<Matrix>();
...
var matrix = new Matrix { MatrixID = matrixID };
matrixRepository.Attach(matrix);
request.Shuttle = matrix;
....

This don’t work. On the attach statement, I got the error: object with the same key already exists in the ObjectStateManager

Does someone can explain me?

Thanks.

Answer 1

At first way, you just find element and put it into matrix. But in second way you try to add matrix which can be already exists in matrixRepository.

EDIT

var matrix = matrixRepository.Find(m => m.MatrixID == matrixID).FirstOrDefault();

this show you that matrixID can be in matrixRepository if not return default.

but here

var matrix = new Matrix { MatrixID = matrixID };
matrixRepository.Attach(matrix); //if matrixRepository allready have matrix with matrixID  you will get error

you just add it to matrixRepository