使用Dynamic LINQ在一对多实体框架关系中的位置

Question

I am using EF 6 and .net 4.5. I have a "Documents" table with the PK "DocumentId" (Int) and another column, "Title". I have another table called "DocumentFilters" with the columns "DocumentId" (Int) and "DocGUID" (Guid). There is a FK on "Doc Id" between the two tables. It is a one to many Id's relationship between the Documents and DocumentFilters tables. The Model looks like this:

I'm trying to write a Dynamic LINQ query using the DynamicLibrary.cs library from the NuGet package.

With regular Linq, the query looks something like this in c#:

DocDBContext db = new DocDBContext();
var documents = db.Documents.Include(d => d.DocumentFilters);
Guid gTest = Guid.Parse("xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx");

documents = documents.Where(d => d.DocumentFilters.Select(f => f.DocGUID).Contains(gTest));

This works perfectly and retrieves the documents delimited by the GUID filter that I'm interested in. However, I need to place this within a filter string dynamically, where it may contain other filters. Is it possible to do that? I've tried code like:

documents = documents.Where("DocumentFilters.Select(DocGUID).Contains(@0)", gTest);

Error: No applicable aggregate method 'Select' exists

or

documents = documents.Where("DocumentFilters.DocGUID=@0", gTest);

Error: GUID property does not exist on DocumentFilters. (Which makes sense because DocumentFilters is a collection).

I also thought it might be worth to give this a shot:

documents = documents.Where("DocumentFilters.AsQueryable().Select(DocGUID).Contains(@0)", gTest);

But again, it doesn't look like the library supports AsQueryable and throws Error: No applicable aggregate method 'AsQueryable' exists.

Is it possible to write such a restriction on a property of an enumerable object within the Documents table?

Answer 1

So one solution was to modify Dynamic.cs by adding " Select " to the IEnumerableSignatures interface in the ExpressionParser class. And additionally add it to the ParseAggregate() method:

if (signature.Name == "Min" || signature.Name == "Max")
        {
            typeArgs = new Type[] { elementType, args[0].Type };
        }
        else if (signature.Name == "Select")
        {
            typeArgs = new Type[] { elementType, Expression.Lambda(args[0], innerIt).Body.Type };
        } 

However, after this I still needed to overload the Contains() method to work with GUIDs. I didn't bother to do that. Instead I realized I can simply use the already supported .Any() instead of .Select() !

documents = documents.Where("DocumentFilters.Any(DocGUID.Equals(@0))", gTest); //!!!

I also had to change the column name from " GUID " to " DocGUID " because when writing GUID.Equals() in the restriction string, the parser mistook it for the GUID type and not the column name, and threw the error that Equals() is not a valid extension for the type GUID.

Sorry for wasting everyone's time!

Answer 2

尝试使用Dynamic Linq ，它可以用于对抗字符串。