如何针对集合调用 Expression<Func<Entity, bool>>

Question

我有一个从存储库模式定义存储库的接口：

interface IRepository
{
    List<Customer> GetAllCustomers(Expression<Func<Customer, bool>> expression);
}

我已经针对 Entity Framework 实施了它：

class EntityFrameworkRepository
{
    public List<Customer> GetAllCustomers(Expression<Func<Customer, bool>> expression)
    {
        return DBContext.Customers.Where(expression).ToList();
    }
}

这似乎工作得很好，它允许我做类似的事情：

var customers = entityFrameworkRepository.Where(
    customer => String.IsNullOrEmpty(customer.PhoneNumber)
);

现在我想要一个用于测试和演示目的的 InMemoryRepository。我试图创建一个：

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?
    }
}

正如您在上面的代码中看到的，我对如何实现 InMemoryRepository.GetAllCustomers 感到困惑。我应该怎么做才能通过提供的表达式和 return 结果过滤客户？

我试过了：

return Customers.Where(expression));

但显然它期待 Func<KeyValuePair<int, Customer>, bool> 所以我得到一个编译错误：

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

Answer 1

尝试.AsQueryable()方法：

return Customers.Values.AsQueryable().Where(expression);

Answer 2

例子

Expression<Func<Products, bool>> expresionFinal = p => p.Active;

if (mydate.HasValue)
{
    Expression<Func<Products, bool>> expresionDate = p => (EntityFunctions.TruncateTime(c.CreatedDate) <= mydate);
    expresionFinal = PredicateBuilder.And(expresionFinal, expresionDate );
}

IQueryable<T> query = dbSet;


    query = query.Where(expresionFinal);

如何针对集合调用 Expression<Func<Entity, bool>>

How to invoke Expression<Func<Entity, bool>> against a collection

c#

linq

iqueryable

func