在LINQ查询语句中预先定义的表达式

Question

是否可以在LINQ表达式中使用先前定义的expressionquery syntax？我创造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; } 
} 

我使用C＃5和EF 5

Answer 1

你可以只使用where isTablet.Compile()(c)。您可能想缓存编译后的版本。