CODEWITHSUNDEEP
linq-to-sql
dovid
dovid

Reputation: 6481

NotSupportedException on concat two IQueryable from same source

See the following code:

var source = Peoples.AsQueryable();
IQueryable<People> p;
p = source.Where( x => false);
p = p.Concat(source.Where( x => x.FirstName == "DAVID"));
p = p.Concat(source.Where(x => x.City_id == 3));
p.Dump(); //I use linqpad but it does not matter now

this code work, and linq2sql product one sql-statement (with three qouery and UNION ALL).

now the same code, ostensibly exactly the same procedure, in another variation, throw NotSupportedException:

var q = new IQueryableUnderstand<People>(Peoples.AsQueryable());
q.AddToList(x => x.City_id == 3);
q.AddToList(x => x.FirstName == "Dave");
q.Results().Dump();

IQueryableUnderstand Class:

class IQueryableUnderstand<T>
{
    IQueryable<T> _source;
    IQueryable<T> combin;

    public IQueryableUnderstand(IQueryable<T> source)
    {
        _source = source;
        combin = _source.Where(s => false);
    }

    public void AddToList(Func<T, bool> predicate) => combin = combin.Concat(_source.Where(predicate));

    public IQueryable<T> Results() => combin;
}

LINQ To SQL exception: Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains operator

I feel stupid, what's the difference?

Upvotes: 1

Views: 61

Answers (1)

Jeff Mercado
Jeff Mercado

Reputation: 134571

Your AddToList() method accepts a Func<T, bool> predicate. The parameter type is incorrect. If applied to your query, it will convert it to a Linq-To-Objects query. IQueryable<TSource> expects expressions, not delegates.

Change your method signature:

public void AddToList(Expression<Func<T, bool>> predicate) =>
    combin = combin.Concat(_source.Where(predicate));

Upvotes: 1

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