How to Combine Logical Expressions in C# Expression?

In the C#expression, combine logic expression

When you have two

type expressions, you may need to use logical operators (such as AND, OR, or not) to combine them. This article discusses various methods to achieve this goal.

Expression<Func<bool>> The same parameter instance

If the two expressions use the same , the combination is simple:

ParameterExpression This is also applicable to negating a single operation:

var body = Expression.AndAlso(expr1.Body, expr2.Body);
var lambda = Expression.Lambda<Func<bool>>(body, expr1.Parameters[0]);

<的> Different parameter examples

static Expression<Func<bool>> Not<T>(
    this Expression<Func<bool>> expr)
{
    return Expression.Lambda<Func<bool>>(
        Expression.Not(expr.Body), expr.Parameters[0]);
}

If the expression uses different parameter instances, you can use to combine:

This method is also applicable to Invoke and

.

static Expression<Func<bool>> AndAlso<T>(
    this Expression<Func<bool>> left,
    Expression<Func<bool>> right)
{
    var param = Expression.Parameter(typeof(T), "x");
    var body = Expression.AndAlso(
            Expression.Invoke(left, param),
            Expression.Invoke(right, param)
        );
    var lambda = Expression.Lambda<Func<bool>>(body, param);
    return lambda;
}

<用> General method OrElse Not

In order to deal with these two situations, one general method can detect which parameters match and select the appropriate combination method:

EF compatibility

From the .NET 4.0,

static Expression<Func<bool>> AndAlso<T>(
    this Expression<Func<bool>> expr1,
    Expression<Func<bool>> expr2)
{
    ParameterExpression param = expr1.Parameters[0];
    if (ReferenceEquals(param, expr2.Parameters[0]))
    {
        return Expression.Lambda<Func<bool>>(
            Expression.AndAlso(expr1.Body, expr2.Body), param);
    }
    return Expression.Lambda<Func<bool>>(
        Expression.AndAlso(
            expr1.Body,
            Expression.Invoke(expr2, param)), param);
}

provided a mechanism to build an EF compatible expression:

By selecting a method that is consistent with your specific scene, you can effectively combine the logical expression in the

instance.

The above is the detailed content of How to Combine Logical Expressions in C# Expression?. For more information, please follow other related articles on the PHP Chinese website!