正如我在评论中所写,存在两个不同的问题:
你必须使用Expression.OrElse
, 因为Expression.Or
is the |
操作员。
但真正的问题是你无法连接 Lambda 表达式(predicate1
, 2
, 3
) 以这种方式。连接表达式很复杂,因为输入参数predicate1
, 2
, 3
是不同的(就像是e1
, e2
, e3
代替e
), and pred1
and pred2
将有一个e4
and e5
输入参数,因此您必须替换某些表达式。
解决方案:
// Note that we only need the Body!
Expression pred1 = Expression.OrElse(Expression.OrElse(predicate1.Body, predicate2.Body), predicate3.Body);
// We change all the predicate2.Parameters[0] to predicate1.Parameters[0] and
// predicate3.Parameters[0] to predicate1.Parameters[0]
var replacer = new SimpleExpressionReplacer(
/* from */ new[] { predicate2.Parameters[0], predicate3.Parameters[0] },
/* to */ new[] { predicate1.Parameters[0], predicate1.Parameters[0] });
pred1 = replacer.Visit(pred1);
// We use for the new predicate the predicate1.Parameters[0]
var pred2 = Expression.Lambda<Func<T, bool>>(pred1, predicate1.Parameters[0]);
var result = queryable.Where(pred2);
and the SimpleExpressionReplacer
:
// A simple expression visitor to replace some nodes of an expression
// with some other nodes
public class SimpleExpressionReplacer : ExpressionVisitor
{
public readonly Dictionary<Expression, Expression> Replaces;
public SimpleExpressionReplacer(Dictionary<Expression, Expression> replaces)
{
Replaces = replaces;
}
public SimpleExpressionReplacer(IEnumerable<Expression> from, IEnumerable<Expression> to)
{
Replaces = new Dictionary<Expression, Expression>();
using (var enu1 = from.GetEnumerator())
using (var enu2 = to.GetEnumerator())
{
while (true)
{
bool res1 = enu1.MoveNext();
bool res2 = enu2.MoveNext();
if (!res1 || !res2)
{
if (!res1 && !res2)
{
break;
}
if (!res1)
{
throw new ArgumentException("from shorter");
}
throw new ArgumentException("to shorter");
}
Replaces.Add(enu1.Current, enu2.Current);
}
}
}
public SimpleExpressionReplacer(Expression from, Expression to)
{
Replaces = new Dictionary<Expression, Expression> { { from, to } };
}
public override Expression Visit(Expression node)
{
Expression to;
if (node != null && Replaces.TryGetValue(node, out to))
{
return base.Visit(to);
}
return base.Visit(node);
}
}