如何调用表达式来; Func键<实体,布尔>>针对集合 [英] How to invoke Expression<Func<Entity, bool>> against a collection
问题描述
我有一个从系统信息库模式定义了存储库的接口:
接口IRepository
{
文件清单<客户> GetAllCustomers(表达式来; Func键<客户,布尔>>表达式);
}
我实现了这对实体框架:
类EntityFrameworkRepository
{
公开名单<客户> GetAllCustomers(表达式来; Func键<客户,布尔>>表达式)
{
返回DBContext.Customers.Where(表达).ToList();
}
}
这似乎运作良好,它可以让我做是这样的:
VAR的客户= entityFrameworkRepository.Where(
客户= GT; String.IsNullOrEmpty(customer.PhoneNumber)
);
现在我想有用于测试和演示目的的InMemoryRepository。我试图创建一个:
类InMemoryRepository
{
字典< INT,客户和GT;客户{搞定;设置;} =新词典< INT,客户和GT;();
公开名单<客户> GetAllCustomers(表达式来; Func键<客户,布尔>>表达式)
{
//什么我放在这里?
}
}
正如你可以在上面的代码中所看到的,我米难倒什么为 InMemoryRepository.GetAllCustomers
的实施做。 ?我应该在那里做了提供表达式过滤客户并返回结果。
我试过:
返回Customers.Where(表达));
但很明显,它期待 Func键< KeyValuePair< INT,客户>中布尔> ;
,所以我得到一个编译错误:
错误CS1929'字典'不包含'在哪里的定义'和最佳推广方法重载'Queryable.Where(IQueryable的,表达式>)'需要类型的接收器的IQueryable'DataAccess.InMemory
块引用>
解决方案尝试的 .AsQueryable()方法的:
返回Customers.Values.AsQueryable(),其中(表达);
I have an interface that defines a repository from the Repository pattern:
interface IRepository { List<Customer> GetAllCustomers(Expression<Func<Customer, bool>> expression); }
I've implemented it against Entity Framework:
class EntityFrameworkRepository { public List<Customer> GetAllCustomers(Expression<Func<Customer, bool>> expression) { return DBContext.Customers.Where(expression).ToList(); } }
That seems to work well, it allows me to do something like:
var customers = entityFrameworkRepository.Where( customer => String.IsNullOrEmpty(customer.PhoneNumber) );
Now I'd like to have an InMemoryRepository for testing and demo purposes. I attempted to create one:
class InMemoryRepository { Dictionary<int, Customer> Customers {get; set;} = new Dictionary<int, Customer>(); public List<Customer> GetAllCustomers(Expression<Func<Customer, bool>> expression) { //what do I put here? } }
As you can see in the above code, I'm stumped on what to do for
InMemoryRepository.GetAllCustomers
implementation. What should I do there to filter the Customers by the provided expression and return the results?I tried:
return Customers.Where(expression));
But obviously it's expecting a
Func<KeyValuePair<int, Customer>, bool>
so I get a compilation error:Error CS1929 'Dictionary' does not contain a definition for 'Where' and the best extension method overload 'Queryable.Where(IQueryable, Expression>)' requires a receiver of type 'IQueryable' DataAccess.InMemory
解决方案Try .AsQueryable() method:
return Customers.Values.AsQueryable().Where(expression);
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