c# - 使用实体框架运行 IQueryable

Question

我正在使用 C# 和 .NET Framework 4.0 开发 Entity Framework Code First 4.4.0.0 库。

我正在搜索如何使用 where 子句上的数组动态创建查询。我发现了这个（在这里）：

IQueryable<Product> SearchProducts (params string[] keywords)
{
  IQueryable<Product> query = dataContext.Products;

  foreach (string keyword in keywords)
  {
    string temp = keyword;
    query = query.Where (p => p.Description.Contains (temp));
  }
  return query;
}

但我不知道如何使用它。如何运行此查询？

我通常这样做：

using (var context = new MyContext())
{
    context.Configuration.ProxyCreationEnabled = false;

    var users = from u in context.Users.Include("WhoHasBlockedMe").Include("Friends")
                from act in u.WantsToDo
                where act.ActivityId == activityId &&
                    u.Gender == genderId &&
                    u.City == city &&
                    u.Country == countryIsoCode
                select u;

    // This user doesn't exit on database
    if ((users == null) ||
        (users.Count() == 0))
    {
        ctx.StatusCode = System.Net.HttpStatusCode.NotFound;
        ctx.SuppressEntityBody = true;
    }
    else
    {
        usersList = new List<UserProfile>();
        foreach(User us in users.ToList())
        {
            usersList.Add(UserProfile.CreateUserView(us, userId));
        }
        ctx.StatusCode = System.Net.HttpStatusCode.OK;
    }
}

如何运行该查询？

Answer 1

您应该执行查询并获得结果：

query.ToList()

在您的示例中，它看起来像这样：

var users = SearchProducts().ToList();
if ((users == null) || (users.Count() == 0))
{
    ctx.StatusCode = System.Net.HttpStatusCode.NotFound;
    ctx.SuppressEntityBody = true;
}
else
{
    usersList = new List<UserProfile>();
    foreach(User us in users)
    {
        usersList.Add(UserProfile.CreateUserView(us, userId));
    }
    ctx.StatusCode = System.Net.HttpStatusCode.OK;
}