我正试图摆脱实体框架,因为除了我们的解决方案中的SQL服务器数据库之外,我必须支持HANA数据库。
我正在用小巧玲珑进行一些研究,所以我用一些虚构的场景创建了一个快速测试环境。
我有以下POCO类似于我的数据库架构(我有更多,但我限于显示这些为简单):
public class Adopter
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Address { get; set; }
public string Address2 { get; set; }
public string City { get; set; }
public State State { get; set; }
public int StateId { get; set; }
public string Zip { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public string Fax { get; set; }
public IEnumerable<Pet> Pets { get; set; }
}
public class State
{
public int Id { get; set; }
public string Name { get; set; }
public string Abreviation { get; set; }
}
public class Pet
{
public int Id { get; set; }
public string IdTag { get; set; }
public string Name { get; set; }
public DateTime AdmitionDate { get; set; }
public Status Status { get; set; }
public int StatusId { get; set; }
public string Notes { get; set; }
public DateTime AdoptionDate { get; set; }
public bool IsAdopted { get; set; }
public int? AdopterId { get; set; }
public int Age { get; set; }
public decimal Weight { get; set; }
public string Color { get; set; }
public Breed Breed { get; set; }
public int BreedId { get; set; }
public Gender Gender { get; set; }
public int GenderId { get; set; }
public IEnumerable<PetImage> PetImages { get; set; }
}
public class Status
{
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
}
public class Gender
{
public int Id { get; set; }
public string Name { get; set; }
}
我在存储库中使用以下命令返回所有采用者的列表:
using (SqlConnection connection = new SqlConnection(_connectionString))
{
var adopters = connection.Query<Adopter>("SELECT a.* FROM Adopters a");
foreach (var adopter in adopters)
{
adopter.State = connection.QueryFirst<State>("Select s.* FROM States s WHERE s.Id = @Id", new { Id = adopter.StateId });
adopter.Pets = connection.Query<Pet>("Select p.* FROM Pets p WHERE p.AdopterId = @Id", new { Id = adopter.Id });
foreach (var pet in adopter.Pets)
{
pet.Status = connection.QueryFirst<Status>("Select s.* FROM Status s WHERE s.Id = @Id", new { Id = pet.StatusId });
pet.Gender = connection.QueryFirst<Gender>("Select g.* FROM Genders g WHERE g.Id = @Id", new { Id = pet.GenderId });
}
}
return adopters;
}
如您所见,我正在基于前一个POCO单独检索每个POCO的数据,并在代码中手动执行联接。
这是正确的方法吗?或者我应该使用多个连接进行大查询并通过dapper和LINQ以某种方式映射结果?
实际解决方案的一个可能的改进是使用QueryMultiple扩展,如下所示:
using (SqlConnection connection = new SqlConnection(_connectionString))
{
string query = @"SELECT * FROM Adopters;
SELECT * FROM States;
SELECT * FROM Pets;
SELECT * FROM Status;
SELECT * FROM Genders;";
using (var multi = connection.QueryMultiple(query, null))
{
var adopters = multi.Read<Adopter>();
var states = multi.Read<State>();
var pets = multi.Read<Pet>();
var statuses = multi.Read<Status>();
var genders = multi.Read<Gender>();
foreach (Adopter adp in adopters)
{
adp.State = states.FirstOrDefault(x => x.Id == adp.StateID);
adp.Pets = pets.Where(x => x.IsAdopted &&
x.AdopterID.HasValue &&
x.AdopterID.Value == adp.AdopterID)
.ToList();
foreach(Pet pet in adp.Pets)
{
pet.Status = statuses.FirstOrDefault(x => x.Id == pet.StatusID);
pet.Gender = genders.FirstOrDefault(x => x.Id == pet.GenderID);
}
}
}
}
这里的好处是您只需一次访问数据库,然后处理内存中的所有内容。
但是,如果你有一个非常大的数据要检索(并且从远程位置),这可能是性能损失和内存瓶颈。最好仔细研究这种方法,并尽可能尝试某种异步处理和/或分页。