Linq exception on Provider.CreateQuery

Question

Given this class:

class SomeClass
{
    public int SomeValue { get; set; }
}

The following list:

var queryableData = new List<SomeClass>() {
    new SomeClass{SomeValue=1 },
    new SomeClass{SomeValue=2 },
    new SomeClass{SomeValue=3 },
    new SomeClass{SomeValue=4 },
    new SomeClass{SomeValue=5 },
    new SomeClass{SomeValue=6 },
    new SomeClass{SomeValue=7 },
}.AsQueryable();

And this code where i try to dinamically query the list (note that the string query could contain anything such as Take,Select,OrderBy, etc).

var externals = new Dictionary<string, object>();
externals.Add("SomeClass", queryableData);

string query = "SomeClass.Where(o => o.SomeValue >= 3)"; // or any query

// here i use the code from System.Linq.Dynamic
var expression = DynamicExpression.Parse(typeof(IQueryable<SomeClass>), query, new[] { externals });
// result will have five values
var result = queryableData.Provider.CreateQuery<SomeClass>(expression);

// here i use the code from System.Linq.Dynamic.Core
var expression2 = DynamicExpressionParser.ParseLambda(typeof(IQueryable<SomeClass>), query, new[] { externals });
// will throw exception here: Argument expression is not valid
var result2 = queryableData.Provider.CreateQuery<SomeClass>(expression2).ToDynamicArray();

I want to know what am i doing wrong that the Provider.CreateQuery is thowing the "Argument expression is not valid" exception?

Which of the two Provider.CreateQuery lines is throwing the exception, result or result2? — Edward, Feb 11 '19 at 18:16
The last parameter to DynamicExpression.Parse / DynamicExpressionParser.ParseLambda are the substitution values, not the data source; in your example you have no substitution values. so you should omit this parameter. — Edward, Feb 11 '19 at 18:17
@Edward, that's true, it was just some leftovers from a bigger code section simplified put it here. — John, Feb 12 '19 at 00:15

score 2 · Accepted Answer · answered Feb 11 '19 at 18:28

The difference with DynamicExpression.Parse (hence the cause of the problem) is that the DynamicExpressionParser.ParseLambda method returns LambdaExpression (basically Expression<Func<TResult>>) which is not a valid query expression.

But the Body of it is, so the simplest fix is to use

var result2 = queryableData.Provider.CreateQuery<SomeClass>(expression2.Body);

Alternatively you could use System.Linq.Dynamic.Core.Parser.ExpressionParser class directly:

var expression2 = new ExpressionParser(null, query, new[] { externals }, null)
    .Parse(typeof(IQueryable<SomeClass>));
var result2 = queryableData.Provider.CreateQuery<SomeClass>(expression2);

Linq exception on Provider.CreateQuery

1 Answers1