PredicateBuilder reusable DateTime predicate setter

Question

I'm using PredicateBuilder to generate dynamic search clauses. In the sample code below, is there a way that I can modify SetDateTimePredicate so it can be used for any DateTime property on SomeType?

Expression<Func<SomeType, bool>> somePredicate = null;
somePredicate = somePredicate.Or(
    SetDateTimePredicate(comparisonOperator, dateTime1, dateTime2));

private Expression<Func<SomeType, bool>> SetDateTimePredicate(
    Enums.ComparisonOperator comparison,
    DateTime dateTime1,
    DateTime dateTime2)
{
    switch (comparison)
    {
        case Enums.ComparisonOperator.IsLessThan:
            return p => p.SomeDateProperty < dateTime1;
        case Enums.ComparisonOperator.IsLessThanOrEqualTo:
            return p => p.SomeDateProperty <= dateTime1;
        case Enums.ComparisonOperator.IsGreaterThan:
            return p => p.SomeDateProperty  > dateTime1;
        case Enums.ComparisonOperator.IsGreaterThanOrEqualTo:
            return p => p.SomeDateProperty >= dateTime1;
        case Enums.ComparisonOperator.IsBetween:
            return p => p.SomeDateProperty >= dateTime1 
                     && p.SomeDateProperty <= dateTime2;
        default:
            return p => p.SomeDateProperty == dateTime1;
    }
}

I tried an extension method but get this error:

System.NotSupportedException occurred
Message="Method 'Boolean Compare(System.DateTime, ComparisonOperator, System.DateTime, System.DateTime)' has no supported translation to SQL."

Extension method:

public static bool Compare(
    this DateTime dateToCompare,
    Enums.ComparisonOperator comparison,
    DateTime dateTime1,
    DateTime dateTime2)
{
    switch (comparison)
    {
        case Enums.ComparisonOperator.IsLessThan:
            return dateToCompare < dateTime1;
        case Enums.ComparisonOperator.IsLessThanOrEqualTo:
            return dateToCompare <= dateTime1;
        case Enums.ComparisonOperator.IsGreaterThan:
            return dateToCompare > dateTime1;
        case Enums.ComparisonOperator.IsGreaterThanOrEqualTo:
            return dateToCompare >= dateTime1;
        case Enums.ComparisonOperator.IsBetween:
            return dateToCompare >= dateTime1
                && dateToCompare <= dateTime2;
        default:
            return dateToCompare == dateTime1;
    }
}

Sample with extension method:

somePredicate = somePredicate.Or(
    p => p.SomeDateProperty.Compare(comparisonOperator, dateTime1, dateTime2));

I tested the first method and it worked. Can you post more context? — Adrian Iftode, Apr 27 '12 at 08:25
Yes, the SetDateTimePredicate method works for me as well. I'm wanting to alter it so that it will accept any DateTime property on my type (and not be "hard-coded" for SomeDateProperty). Or if there's a different way to accomplish the same thing, that would be fine, too. I tried an extension method but got the error I mentioned. — user1360192, Apr 27 '12 at 17:37

Daniel Baker · Answer 1 · 2012-05-09T14:11:44.127

Below is a generic solution, that could be used for any type that has the comparison operators defined not just DateTime. I made the methods, extension methods on the Enum.ComparisionOperator type. It would be used like:

Expression<Func<SomeType, bool>> somePredicate = comparisonOperator.Compare(
    (SomeType p) => p.SomeDateProperty, dateTime1, dateTime2));

The methods defined as:

public static Expression<Func<TSource, bool>> Compare<TSource, TValue>(
    this Enums.ComparisonOperator comparison,
    Expression<Func<TSource, TValue>> source,
    TValue value1, TValue value2)
{
    var value1Expr = Expression.Constant(value1);
    var value2Expr = Expression.Constant(value2);
    var newExpr = comparison.CompareExpr(source.Body, value1Expr, value2Expr);
    return Expression.Lambda<Func<TSource, bool>>(newExpr, source.Parameters);
}
public static Expression CompareExpr(
    this Enums.ComparisonOperator comparison,
    Expression exprLeft,
    Expression exprRight1, Expression exprRight2)
{
    switch (comparison)
    {
        case Enums.ComparisonOperator.IsLessThan:
            return Expression.LessThan(exprLeft, exprRight1);
        case Enums.ComparisonOperator.IsLessThanOrEqualTo:
            return Expression.LessThanOrEqual(exprLeft, exprRight1);
        case Enums.ComparisonOperator.IsGreaterThan:
            return Expression.GreaterThan(exprLeft, exprRight1);
        case Enums.ComparisonOperator.IsGreaterThanOrEqualTo:
            return Expression.GreaterThanOrEqual(exprLeft, exprRight1);
        case Enums.ComparisonOperator.IsBetween:
            return Expression.AndAlso(
                Expression.GreaterThanOrEqual(exprLeft, exprRight1),
                Expression.LessThanOrEqual(exprLeft, exprRight2));
        default:
            return Expression.Equal(exprLeft, exprRight1);
    }
}

Edit: I changed the methods above to be generic.

PredicateBuilder reusable DateTime predicate setter

1 Answers1