问题描述
我创建了一个可过滤的BindingList 。它的效果很好：
I created a filterable BindingList from this source. It works great:
list.Filter("Customer == 'Name'");
做什么应该内部工作就像解析器一样，将表达式 == 或！= 转换为系统.Linq.Expressions.Expression 。在这种情况下， == 成为 System.Linq.Expressions.Expression.Equal 。
does what it should. The internals work like a parser, that converts the expression == or != into System.Linq.Expressions.Expression. In this case, == becomes System.Linq.Expressions.Expression.Equal.
不幸的是， System.Linq.Expressions.Expression 不包含类似的操作符，我不知道如何解决这个问题。
Unfortunately System.Linq.Expressions.Expression does not contain a like operator and I don't know how to solve this.
初始代码如下所示：
private static Dictionary<String, Func<Expression, Expression, Expression>>
binaryOpFactory = new Dictionary<String, Func<Expression, Expression, Expression>>();
static Init() {
binaryOpFactory.Add("==", Expression.Equal);
binaryOpFactory.Add(">", Expression.GreaterThan);
binaryOpFactory.Add("<", Expression.LessThan);
binaryOpFactory.Add(">=", Expression.GreaterThanOrEqual);
binaryOpFactory.Add("<=", Expression.LessThanOrEqual);
binaryOpFactory.Add("!=", Expression.NotEqual);
binaryOpFactory.Add("&&", Expression.And);
binaryOpFactory.Add("||", Expression.Or);
}
然后我创建了一个可以做我想做的表达式：
Then I created an expression that will do what I want:
private static System.Linq.Expressions.Expression<Func<String, String, bool>>
Like_Lambda = (item, search) => item.ToLower().Contains(search.ToLower());
private static Func<String, String, bool> Like = Like_Lambda.Compile();
例如
Console.WriteLine(like("McDonalds", "donAld")); // true
Console.WriteLine(like("McDonalds", "King")); // false
但是 binaryOpFactory 需要这样：
Func<Expression, Expression, Expression>
预定义的表达式似乎正是这样：
The predefined expressions seem to be exactly that:
System.Linq.Expressions.Expression.Or;
任何人都可以告诉我如何转换我的表达？
Can anyone tell me how to convert my expression?
推荐答案
如下所示：
static IEnumerable<T> WhereLike<T>(
this IEnumerable<T> data,
string propertyOrFieldName,
string value)
{
var param = Expression.Parameter(typeof(T), "x");
var body = Expression.Call(
typeof(Program).GetMethod("Like",
BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public),
Expression.PropertyOrField(param, propertyOrFieldName),
Expression.Constant(value, typeof(string)));
var lambda = Expression.Lambda<Func<T, bool>>(body, param);
return data.Where(lambda.Compile());
}
static bool Like(string a, string b) {
return a.Contains(b); // just for illustration
}
根据 Func< Expression，Expression，Expression> ：
static Expression Like(Expression lhs, Expression rhs)
{
return Expression.Call(
typeof(Program).GetMethod("Like",
BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public)
,lhs,rhs);
}
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