c# - 如何为Like创建System.Linq.Expressions.Expression？

我创建了一个可过滤的BindingList from this source。效果很好:

list.Filter("Customer == 'Name'");

做它应该做的。内部结构就像解析器一样，将表达式==或!=转换为System.Linq.Expressions.Expression。在这种情况下，==变为System.Linq.Expressions.Expression.Equal。

不幸的是，System.Linq.Expressions.Expression不包含like运算符，而且我不知道该如何解决。

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，我创建了一个表达式，可以执行我想要的操作:

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要求:

Func<Expression, Expression, Expression>

预定义的表达式似乎恰好是:

System.Linq.Expressions.Expression.Or;

谁能告诉我如何转换我的表情？

最佳答案

就像是:

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
}

就Func<Expression,Expression,Expression>而言:

static Expression Like(Expression lhs, Expression rhs)
{
    return Expression.Call(
        typeof(Program).GetMethod("Like",
            BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public)
            ,lhs,rhs);
}

关于c# - 如何为Like创建System.Linq.Expressions.Expression？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/956743/