使用Entity Framework联接表的更好方法

Question

Good morning,

I have inherited a database with no foreign key relations and the project is such that i have to ignore this major issue and work around it. Obviously this eliminates some of the cooler features of Entity Framework providing me related entities automatically.

So i have been forced to do something like this:

using (var db = new MyEntities())
{
    Entities.Info record = db.Infoes.Where(x => x.UserId == authInfo.User.Id).FirstOrDefault();

    //Get all the accounts for the user
    List<Entities.AcctSummary> accounts = db.AcctSummaries.Where(x => x.InfoId == record.Id).ToList();

    //Loop through each account
    foreach (Entities.AcctSummary account in accounts)
    {
        //pull records for account
        List<Entities.Records> records= db.Records.Where(x => x.AcctSummaryId == account.Id).ToList();
    }
}

If there a better way to join the "record" and "accounts" Entities, or perhaps a more efficient way for getting "records" in a single query?

TIA

Answer 1

Are you just looking for the .Join() extension method? As an example, joining Infoes and Accounts might look like this:

var accounts = db.Infoes.Join(db.Accounts,
                              i => i.Id,
                              a => a.InfoId,
                              (info, account) => new { info, account });

This would result in accounts being an enumeration of an anonymous type with two properties, one being the Info record and the other being the Account record. The collection would be the full superset of the joined records.

You can of course return something other than new { info, account } , it works just like anything you'd put into a .Select() clause. Whatever you select from these joined tables would be what you have an enumeration of in accounts . You can further join more tables by changing .Join() extensions, returning whatever you want from each.