EntityFramework按ID过滤列表

Question

I have this function:

[HttpPost]
[Route("")]
/// <summary>
/// Create a team
/// </summary>
/// <param name="model">The team model</param>
/// <returns>The modified team model</returns>
public async Task<IHttpActionResult> Create(TeamBindingViewModel model)
{

    // If our model is invalid, return the errors
    if (!ModelState.IsValid)
        return BadRequest(ModelState);

    // Get all our colours
    var colours = await this.colourService.GetAllAsync();

    // Create our new model
    var team = new Team()
    {
        Name = model.Name,
        Sport = model.Sport
    };

    // For each colour, Add to our team
    team.Colours = colours.Join(model.Colours, c => c.Id, m => m.Id, (c, m) => new Colour { Id = c.Id, Hex = c.Hex, Name = c.Name }).ToList();

    // Create our team
    this.service.Create(team);

    // Save our changes
    await this.unitOfWork.SaveChangesAsync();

    // Assign our Id to our model
    model.Id = team.Id;

    // Return Ok
    return Ok(model);
}

If I run it, then EntityFramework enters new colours into the database rather than referencing the colours. I know this is because I am creating a new Colour in my join. If I change my function to this:

[HttpPost]
[Route("")]
/// <summary>
/// Create a team
/// </summary>
/// <param name="model">The team model</param>
/// <returns>The modified team model</returns>
public async Task<IHttpActionResult> Create(TeamBindingViewModel model)
{

    // If our model is invalid, return the errors
    if (!ModelState.IsValid)
        return BadRequest(ModelState);

    // Get all our colours
    var colours = await this.colourService.GetAllAsync();

    // Create our new model
    var team = new Team()
    {
        Name = model.Name,
        Sport = model.Sport
    };

    // For each colour, Add to our team
    team.Colours = colours;

    // Create our team
    this.service.Create(team);

    // Save our changes
    await this.unitOfWork.SaveChangesAsync();

    // Assign our Id to our model
    model.Id = team.Id;

    // Return Ok
    return Ok(model);
}

Everything works fine. The only thing that is changed in the second snippet is :

team.Colours = colours.Join(model.Colours, c => c.Id, m => m.Id, (c, m) => new Colour { Id = c.Id, Hex = c.Hex, Name = c.Name }).ToList();

became

team.Colours = colours;

which is the list retrieved from the database. EntityFramework knows that this has not been changed so it just references the colours instead of creating new ones. How can I get my filtered list to do the same?

Cheers, /r3plica

Answer 1

Ok, I knew it was simple. I changed the problem line to this:

// For each colour, Add to our team
team.Colours = colours.Where(m => model.Colours.Any(c => c.Id == m.Id)).ToList();