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[英]Convert Expression<Func<T,T,bool>> to Expression<Func<T,bool>>
[英]Join Expression<Func<T,bool>>
我有一個表達式列表:
List<Expression<Func<Domain.FollowUpActivity, bool>>> fuaExpressions = null;
我需要將所有這些都加入一個OR表達式中:我已經嘗試過了:
Expression body = Expression.Constant(false);
foreach (var orExpression in orExpressions)
foreach (Expression orExp in orExpression.Expressions)
body = Expression.Or(body, orExp);
由於在Expression<Boolean>
和Expression<Func<T, bool>>
之間未定義布爾運算符,因此拋出InvalidOperationException
請幫忙嗎?
摘自阿爾巴哈里兄弟的一本好書:
public static class PredicateBuilder
{
public static Expression<Func<T, bool>> True<T> () { return f => true; }
public static Expression<Func<T, bool>> False<T> () { return f => false; }
public static Expression<Func<T, bool>> Or<T> (this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
return Expression.Lambda<Func<T, bool>>
(Expression.OrElse (expr1.Body, invokedExpr), expr1.Parameters);
}
public static Expression<Func<T, bool>> And<T> (this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
return Expression.Lambda<Func<T, bool>>
(Expression.AndAlso (expr1.Body, invokedExpr), expr1.Parameters);
}
}
像這樣使用它:
List<Expression<Func<Domain.FollowUpActivity, bool>>> fuaExpressions = null;
Expression<Func<Domain.FollowUpActivity, bool>> result = PredicateBuilder.False<Domain.FollowUpActivity>();
foreach (var exp in fuaExpressions)
{
result = PredicateBuilder.Or(result, exp);
}
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