找了很久，原來就在 梨子給的範例裡。
假設有兩個 expression: e1, e2
var combineBody = Expression.AndAlso(e1.Body, Expression.Invoke(e2, e1.Parameters[0]));
var finalExpression = Expression.Lambda<Func<TestClass, bool>>(combineBody, e1.Parameters).Compile();
同理，把上面的 AndAlso 換成 OrElse 就可以用 Or 合併。
即使只有兩行，還是不太可能背起來，所以當然要來做一下擴充
public static class ExpressionExtension
{
public static Expression<Func<T, bool>> AndAlso<T>(this Expression<Func<T, bool>> e1, Expression<Func<T, bool>> e2)
{
var combineE = Expression.AndAlso(e1.Body, Expression.Invoke(e2, e1.Parameters[0]));
return Expression.Lambda<Func<T, bool>>(combineE, e1.Parameters);
}
public static Expression<Func<T, bool>> OrElse<T>(this Expression<Func<T, bool>> e1, Expression<Func<T, bool>> e2)
{
var combineE = Expression.OrElse(e1.Body, Expression.Invoke(e2, e1.Parameters[0]));
return Expression.Lambda<Func<T, bool>>(combineE, e1.Parameters);
}
}
使用範例:
Expression<Func<Market, bool>> e1 = e => e.Is_Deleted == isDelete;
Expression<Func<Market, bool>> e2 = e => string.IsNullOrEmpty(marketNo) || e.MarketNo.ToUpper().Contains(marketNo.ToUpper());
return new
{
andMarkets = Ds.PageContext.ShopBandContext.Markets.Where(e1.AndAlso(e2)).ToList(),
orMarkets = Ds.PageContext.ShopBandContext.Markets.Where(e1.OrElse(e2)).ToList(),
};
再補兩個擴充, 可以把多個 Expression 用 AndAlso 或 OrElse 串在一起:
public static Expression<Func<T, bool>> OrElseAll<T>(this IEnumerable<Expression<Func<T, bool>>> exps)
{
if (exps.Count() == 1)
{
return exps.First();
}
var e0 = exps.First();
var orExp = exps.Skip(1).Aggregate(e0.Body, (x, y) => Expression.OrElse(x, Expression.Invoke(y, e0.Parameters[0])));
return Expression.Lambda<Func<T, bool>>(orExp, e0.Parameters);
}
public static Expression<Func<T, bool>> AndAlsoAll<T>(this IEnumerable<Expression<Func<T, bool>>> exps)
{
if (exps.Count() == 1)
{
return exps.First();
}
var e0 = exps.First();
var orExp = exps.Skip(1).Aggregate(e0.Body, (x, y) => Expression.AndAlso(x, Expression.Invoke(y, e0.Parameters[0])));
return Expression.Lambda<Func<T, bool>>(orExp, e0.Parameters);
}
使用範例:
Expression<Func<Market, bool>> q = e =>
e.Is_Deleted == "N"
&& (string.IsNullOrEmpty(marketNo) || e.MarketNo.ToLower().Contains(marketNo.ToLower()))
&& (string.IsNullOrEmpty(isCombination) || isCombination != "Y" || e.TypeEnum == 200);
if (!string.IsNullOrEmpty(name))
{
var nameList = name.Split(',').Select(e => e.Trim())
.Where(e => !string.IsNullOrEmpty(e));
if (nameList.Any())
{
q = q.AndAlso(nameList
.Select(s => (Expression<Func<Market, bool>>)(e => e.Name.ToLower().Contains(s.ToLower())))
.OrElseAll());
}
}
另外在 google，整理了 stackoverflow 幾篇文章之後得到的另一個方法，比較複雜, 不過可以讓人理解一下 Expression 比較底層的東西，也留下來參考一下。
internal class MergeTool : ExpressionVisitor
{
private readonly ParameterExpression _parameter;
protected override Expression VisitParameter(ParameterExpression node)
{
return base.VisitParameter(_parameter);
}
internal MergeTool(ParameterExpression parameter)
{
_parameter = parameter;
}
public static Expression<Func<T, bool>> MergedExpression<T>(Expression<Func<T, bool>> e1, Expression<Func<T, bool>> e2)
{
ParameterExpression param = Expression.Parameter(typeof(T));
BinaryExpression MergeBody = Expression.AndAlso(e1.Body, e2.Body);
var ReplacedBody = (BinaryExpression)new MergeTool(param).Visit(MergeBody);
return Expression.Lambda<Func<T, bool>>(ReplacedBody, param);
}
}
使用時要 Compile
var mergedExpression = MergeTool.MergedExpression(e1, e2);
var list = testList.Where(mergedExpression.Compile());