我试图摆脱 Entity Framework ,因为我必须在我们的解决方案中支持除 SQL Server 数据库之外的 HANA 数据库。
我正在对 dapper 进行一些研究,因此我创建了一个包含一些虚构场景的快速测试环境。
我有以下类似于我的数据库模式的 POCO(我有更多,但为了简单起见,我仅限于展示这些):
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内容来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,我正在根据前一个 POCO 分别检索每个 POCO 的数据,并在代码中手动执行连接。
这是正确的做法吗?还是我应该使用多个连接执行大型查询并通过 dapper 和 LINQ 以某种方式映射结果?
最佳答案
对您的实际解决方案的可能改进是通过使用 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);
}
}
}
}
这样做的好处是您只需访问数据库一次,然后在内存中处理所有内容。
但是,如果您要检索非常大的数据(并且来自远程位置),这可能会影响性能和内存瓶颈。最好仔细研究这种方法,并在可能的情况下尝试某种异步处理和/或分页。
关于c# - 这是使用 Dapper 的正确方法还是我做错了?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41358302/