这是使用Dapper的正确方法还是我做错了？

Question

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.

我正在用小巧玲珑做一些研究,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？

Answer 1

对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，然后就可以在内存中处理所有内容。

然而，如果您有非常大的数据要检索（并且来自远程位置），这可能会造成性能影响和内存瓶颈。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。