Question

我想使用动态表达式在我的应用中创建高级搜索。我读了一些关于表达式的文章并编写了这段代码：

var result = //my query
    from filter in context.Filters
    join customer in context.Customers on filter.customerId equals customer.id
    select new { customer, filter };

var paramCustomer = Expression.Parameter(typeof(Models.Customer), "customer");
var paramFilter = Expression.Parameter(typeof(Models.Filter), "filter");
var pName = Expression.Property(paramCustomer, "name");
var pInstallDate = Expression.Property(paramFilter, "installDate");
var con1 = Expression.OrElse(

    Expression.Equal(pName, Expression.Constant("ASD"))
        ,
    Expression.Equal(pInstallDate, Expression.Constant(13920505))

);

var con2 = Expression.AndAlso(

    Expression.Equal(pName, Expression.Constant("ABC"))
        ,
    con1

);

var exp1 = Expression.Lambda<Func<Models.Customer, Models.Filter, bool>>(con2, new ParameterExpression[] { paramCustomer, paramFilter });

Console.WriteLine(
    exp1 //output: (customer, filter) => ((customer.name == "ABC") AndAlso ((customer.name == "ASD") OrElse (filter.installDate == 1392)))
);

Console.WriteLine(
    result.Where(exp1) //error
);

我想在我的查询中添加动态表达式，但是我收到了这些错误：

错误7'System.Linq.IQueryable'不包含'Where'的定义和最佳扩展方法重载'System.Linq.Enumerable.Where（System.Collections.Generic.IEnumerable，System.Func）'具有一些无效的论点

错误8参数2：无法从'System.Linq.Expressions.Expression＆gt;'转换到'System.Func'

“where.Lambda”在“where”返回错误“有一些无效的参数”

0 个答案: