Create predicate with a BinaryExpression containing multiple parameters

Question

is it possible to dynamically generate such a predicate using LambdaExpressions?

Expression> predicate = t =>
    t         


        

Answer 1

I would recommend using nein-linq to combine, build and compose predicates (and many other expression puzzles), or LinqKit

Both support Entity Framework

For example, using nein-linq

Given:

public static class TestExpressions
{
    [InjectLambda]
    public static bool IsTestDateEarlierThan(this Test test, DateTime? dateTime, int numberOfDays)
    {
        return dateTime > test.TestDate.AddDays(numberOfDays);
    }

    public static Expression> IsTestDateEarlierThan()
    {
        return (test, dateTime, numberOfDays) => dateTime > DbFunctions.AddDays(test.TestDate, numberOfDays);
    }

    // Simple caching...
    private static readonly Func _hasAnyLevelDateAfterTestDays = HasAnyLevelDateAfterTestDays().Compile();

    [InjectLambda]
    public static bool HasAnyLevelDateAfterTestDays(this Test test, int numberOfDays)
    {
        return _hasAnyLevelDateAfterTestDays(test, numberOfDays);
    }

    public static Expression> HasAnyLevelDateAfterTestDays()
    {
        return (test, numberOfDays) => test.Levels.Any(l => l.LevelDetails.Any(ld => test.IsTestDateEarlierThan(ld.LevelDate, numberOfDays)));
    }       
}

When:

var testList = new List
{
    new Test {
        Levels = new List {
            new Level {
                LevelDetails = new List {
                    new LevelDetail {
                        LevelDate = DateTime.Today
                    }
                }
            }
        },
        // Not matched
        TestDate = DateTime.Today
    },
    new Test {
        Levels = new List {
            new Level {
                LevelDetails = new List {
                    new LevelDetail {
                        LevelDate = DateTime.Today
                    }
                }
            }
        },
        // Not matched
        TestDate = DateTime.Today.AddDays(-1)
    },
    new Test {
        Levels = new List {
            new Level {
                LevelDetails = new List {
                    new LevelDetail {
                        LevelDate = DateTime.Today
                    }
                }
            }
        },
        // Matched
        TestDate = DateTime.Today.AddDays(-2)
    }
};

Then:

var testQuery = testList.AsQueryable();

// Alternative one
var result1 = testQuery
    .ToInjectable() // Don't forget!!
    .Where(test => test.Levels.Any(l => l.LevelDetails.Any(ld => test.IsTestDateEarlierThan(ld.LevelDate, 1))))
    .ToList();

// Alternative two: You get the point :)
var result2 = testQuery
    .ToInjectable() // Don't forget!!
    .Where(test => test.HasAnyLevelDateAfterTestDays(1))
    .ToList();