Use LinqKit PredicateBuilder for related model (EF Core)

Question

I want to use LinqKit's PredicateBuilder and pass the predicate into .Any method for related model.

So I want to build a predicate:

var castCondition = PredicateBuilder.New<CastInfo>(true);

if (movies != null && movies.Length > 0)
{
    castCondition = castCondition.And(c => movies.Contains(c.MovieId));
}
if (roleType > 0)
{
    castCondition = castCondition.And(c => c.RoleId == roleType);
}

And then use it to filter model that has relation to model in predicate:

IQueryable<Name> result = _context.Name.AsExpandable().Where(n => n.CastInfo.Any(castCondition));
return await result.OrderBy(n => n.Name1).Take(25).ToListAsync();

But this causes a System.NotSupportedException: Could not parse expression 'n.CastInfo.Any(Convert(__castCondition_0, Func``2))': The given arguments did not match the expected arguments: Object of type 'System.Linq.Expressions.UnaryExpression' cannot be converted to type 'System.Linq.Expressions.LambdaExpression'.

I saw similar question and answer there suggests to use .Compile. Or one more question that build an extra predicate.

So I tried to use extra predicate

var tp = PredicateBuilder.New<Name>(true);
tp = tp.And(n => n.CastInfo.Any(castCondition.Compile()));
IQueryable<Name> result = _context.Name.AsExpandable().Where(tp);

Or use compile directly

IQueryable<Name> result = _context.Name.AsExpandable().Where(n => n.CastInfo.Any(castCondition.Compile()));

But I have an error about Compile: System.NotSupportedException: Could not parse expression 'n.CastInfo.Any(__Compile_0)'

So is it possible to convert the result from PredicateBuilder to pass into Any?

Note: I was able to build the desired behavior combining expressions, but I don't like that I need extra variables.

System.Linq.Expressions.Expression<Func<CastInfo,bool>> castExpression = (c => true);
if (movies != null && movies.Length > 0)
{
    castExpression = (c => movies.Contains(c.MovieId));
}
if (roleType > 0)
{
    var existingExpression = castExpression;
    castExpression = c => existingExpression.Invoke(c) && c.RoleId == roleType;
}
IQueryable<Name> result = _context.Name.AsExpandable().Where(n => n.CastInfo.Any(castExpression.Compile()));
return await result.OrderBy(n => n.Name1).Take(25).ToListAsync();

So I assume I just miss something about builder.

Update about versions: I use dotnet core 2.0 and LinqKit.Microsoft.EntityFrameworkCore 1.1.10

Answer 1

It may not be exactly related to the original question, but considering the following model :

public Class Music
{
    public int Id { get; set; }
    public List<Genre> Genres { get; set; }
}
public Class Genre
{
    public int Id { get; set; }
    public string Title { get; set; }
}

List<string> genresToFind = new() {"Pop", "Rap", "Classical"};

If you are trying to find all Musics that their genres exist in genresToFind list, here's what you can do:

Create PredicateBuilder expressions chain on Genre model :

var pre = PredicateBuilder.New<Genre>();
foreach (var genre in genresToFind)
{
    pre = pre.Or(g => g.Title.Contains(genre));
}

Then execute your query like this :

var result = await _db.Musics.AsExpandable()
    .Where(m => m.Genres
        .Any(g => pre.ToExpression().Invoke(g)))
    .ToListAsync();

ToExpression() is a generic extension method that we've created to convert ExpressionStarter<Genre> type to Expression<Func<Genre, bool>> :

public static class ExpressionExtensions
{
    public static Expression<Func<T, bool>> ToExpression<T> (this 
        ExpressionStarter<T> exp) => exp;
}

Also, you'll need LinqKit.Microsoft.EntityFrameworkCore package for efcore.

Answer 2

Delete the type="submit" attribute. This attribute let's the form send.

 <h3> Backtest ID: {{ backtestID }} </h3>
 <div class="row">

     <div class="col-md-1" >
         <form method="post">
             <button class="btn btn-success" 
                     formaction="{{ url_for('results.save_backtest', id=backtestID) }}">Save</button>
         </form>
     </div>

     <div class="col-md-1" >
         <form method="post">
             <button class="btn btn-info" 
                     formaction="{{ url_for('results.rerun_backtest', id=backtestID) }}">Run</button>
         </form>
     </div>

 </div>