1

是否可以在具有查询语法的 LINQ 表达式中使用先前定义的表达式？我创建了一个人为的例子来说明我的问题。

var tabletTypes = new List<int> { 2, 3 };
//I want to use this expression many times
Expression<Func<Computer, bool>> isTablet = comp => tabletTypes.Contains(comp.Type);

var computers = db.Computers;
var producers = db.Producers;

//I know how to use the expression in fluent syntax
IQueryable<Producer> tabletProducers = computers
                               .Where(isTablet)
                               .Join(producers, 
                                     comp => comp.ProducerId, 
                                     producer => producer.Id, 
                                     (comp, producer) => producer);

//How can I use the expression in query syntax
IQueryable<Producer> tabletProducers2 = from c in computers
                                        join p in producers
                                            on c.ProducerId equals p.Id
                                        where /*How can I use isTablet here?*/
                                        select p;


public class Producer
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Computer
{
    public int Id { get;set; }
    public int Type { get; set; }
    public int ProducerId { get; set; }
}

我正在使用 C# 5 和 EF 5。

4

1 回答 1

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你可以只使用where isTablet.Compile()(c). 您可能想要缓存已编译的版本。

于 2013-07-05T16:09:25.400 回答