linq-to-sql 组合表达式

发布于 2024-08-27 14:43:13 字数 746 浏览 5 评论 0 原文

有什么方法可以将表达式列表合并为一个吗？我有 List>; expList 并尝试组合成一个（AndAlso）并获取

Expression<Child, bool> combined = Combine(expList);

组合表达式的预期用法是这样的：

//type of linqFilter is IQueryable<Parent>
linqFilter = linqFilter.SelectMany(p => p.Child).
         Where(combined).Select(t=> t.Parent);

我正在尝试这样的事情：

var result = expList.Cast<Expression>().
Aggregate((p1, p2) => Expression.AndAlso(p1, p2));

但是出现异常

{"The binary operator AndAlso is not defined for the types 'System.Func`2[Child,System.Boolean]' and 'System.Func`2[Child,System.Boolean]'."}

原文

Is there any way I can combine list of expressions into one? I have List<Expression<Child, bool>> expList and trying to combine into one (AndAlso) and get

Expression<Child, bool> combined = Combine(expList);

Intended usage for combined expression is this:

//type of linqFilter is IQueryable<Parent>
linqFilter = linqFilter.SelectMany(p => p.Child).
         Where(combined).Select(t=> t.Parent);

I am trying something like this:

var result = expList.Cast<Expression>().
Aggregate((p1, p2) => Expression.AndAlso(p1, p2));

But getting an exception

{"The binary operator AndAlso is not defined for the types 'System.Func`2[Child,System.Boolean]' and 'System.Func`2[Child,System.Boolean]'."}

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淑女气质 2024-09-03 14:43:13

尝试一下它是一个构建器，因此您必须为 expList 中的每个递归调用它

public Expression<Func<T, bool>> Combine<T>(Expression<Func<T, Boolean>> first, Expression<Func<T, Boolean>> second)
{
   var toInvoke = Expression.Invoke(second, first.Parameters);

   return (Expression<Func<T, Boolean>>)Expression.Lambda(Expression.AndAlso(first.Body, toInvoke), first.Parameters);
}

Try this its a builder so you would have to recursively call it for each in expList

public Expression<Func<T, bool>> Combine<T>(Expression<Func<T, Boolean>> first, Expression<Func<T, Boolean>> second)
{
   var toInvoke = Expression.Invoke(second, first.Parameters);

   return (Expression<Func<T, Boolean>>)Expression.Lambda(Expression.AndAlso(first.Body, toInvoke), first.Parameters);
}

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