c# - PredicateBuilder 可重用 DateTime 谓词 setter

Question

我正在使用 PredicateBuilder生成动态搜索子句。在下面的示例代码中，有没有一种方法可以修改 SetDateTimePredicate，以便它可以用于 SomeType 上的任何 DateTime 属性？

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;
    }
}

我尝试了一种扩展方法但得到了这个错误:

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

扩展方法:

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;
    }
}

带有扩展方法的示例:

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

Answer 1

下面是一个通用的解决方案，它可以用于任何定义了比较运算符的类型，而不仅仅是 DateTime。我在 Enum.ComparisionOperator 类型上创建了方法和扩展方法。它会像这样使用:

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

方法定义为:

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);
    }
}

编辑:我将上面的方法更改为通用方法。