C# 如何将两个表达式组合成一个新表达式？
我有两个表达式：
public static Expression<Func<int, bool>> IsDivisibleByFive() {
return (x) => x % 5 == 0;
}
and
public static Expression<Func<int, bool>> StartsWithOne() {
return (x) => x.ToString().StartsWith("1");
}
我想创建一个同时应用这两个表达式的新表达式（相同的表达式以不同的组合在我的代码中使用）：
public static Expression<Func<int, bool>> IsValidExpression() {
return (x) => IsDivisibleByFive(x) && StartsWithOne(x);
}
然后执行：
public static class IntegerExtensions
{
public static bool IsValid(this int self)
{
return IsValidExpression().Compile()(self);
}
}
在我的代码中：
if (32.IsValid()) {
//do something
}
我有很多我想要的这样的表达式定义一次而不是到处重复代码。
谢谢。
I have two expressions:
public static Expression<Func<int, bool>> IsDivisibleByFive() {
return (x) => x % 5 == 0;
}
and
public static Expression<Func<int, bool>> StartsWithOne() {
return (x) => x.ToString().StartsWith("1");
}
And I want to create a new expression that applies both at once (the same expressions are used all over my code in different combinations):
public static Expression<Func<int, bool>> IsValidExpression() {
return (x) => IsDivisibleByFive(x) && StartsWithOne(x);
}
Then do:
public static class IntegerExtensions
{
public static bool IsValid(this int self)
{
return IsValidExpression().Compile()(self);
}
}
And in my code:
if (32.IsValid()) {
//do something
}
I have many such expressions that I want to define once instead of duplicating code all over the place.
Thanks.
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如果您只是尝试将表达式主体与
AndAlso表达式组合，您将遇到的问题是x参数表达式实际上是两个不同的参数（即使它们具有同名）。为此，您需要使用表达式树访问器来替换要与单个通用ParameterExpression组合的两个表达式中的x。您可能需要查看 Joe Albahari 的 PredicateBuilder 库，它会为您完成繁重的工作。结果应该类似于：
The problem you'll run into if you just try combining the expression bodies with an
AndAlsoexpression is that thexparameter expressions are actually two different parameters (even though they have the same name). In order to do this, you would need to use an expression tree visitor to replace thexin the two expressions you want to combine with a single, commonParameterExpression.You may want to look at Joe Albahari's PredicateBuilder library, which does the heavy lifting for you. The result should look something like: