Question

我试图在没有单个根实体的情况下获取多个实体（实体关系的有向图只是弱连接图，没有强连接）我无法弄清楚如何做它在Nhibernates QueryOver api（或Linq，但似乎更弱）

这些是我的关系：

ClientTaxEntity引用了1 Client和N Manufacturers

InstructionTemplate引用了1 Client和1 Manufacturer

我希望获得所有可能的客户端 - 制造商对的结果（可能=它们在ClientTaxEntity中一起）并获取模板（如果存在）（否则为null）

这是我到目前为止所尝试的：

        Client client = null;
        Manufacturer manufacturer = null;
        InstructionTemplate template = null;
        ClientTaxEntity taxEntity = null;

        InstructionTemplateInfo info = null;

        var query =Session.QueryOver<ClientTaxEntity>(() => taxEntity)
                   .JoinAlias(x => x.Client, () => client)
                   .JoinAlias(x => x.Manufacturers, () => manufacturer)
                   .Left
                   .JoinQueryOver(() => template, () => template,() => template.Client == client && template.Manufacturer == manufacturer);
        var result = query
            .SelectList(builder => builder
                        .Select(() => client.Name).WithAlias(() => info.ClientName)
                        .Select(() => client.Id).WithAlias(() => info.ClientId)
                        .Select(() => manufacturer.Name).WithAlias(() => info.ManufacturerName)
                        .Select(() => manufacturer.Id).WithAlias(() => info.ManufacturerId)
                        .Select(() => template.Id).WithAlias(() => info.TemplateId)
                        .Select(() => template.Type).WithAlias(() => info.Type)
            )
            .TransformUsing(Transformers.DistinctRootEntity)
            .TransformUsing(Transformers.AliasToBean<InstructionTemplateInfo>())
            .List<InstructionTemplateInfo>();

info对象是我想要的结果。

但是语法.JoinQueryOver(() => template似乎对路径参数无效（例外情况说：could not resolve property: template of: ClientTaxEntity

Answer 1

要在SQL中编写查询时获得所需的结果，有必要写下以下内容：

SELECT Client_Id, Client_Name, Manufacturer_Id, Manufacturer_Name
FROM
(
  SELECT Client.Id as Client_Id, Client.Name as Client_Name, 
         Manufacturer.Id as Manufacturer_Id, Manufacturer.Name as Manufacturer_Name
  FROM ClientTax
  INNER JOIN Client on Client.Id = ClientTax.Client_Id
  INNER JOIN Manufacturer on Manufacturer.Id = Manufacturer.Manufacturer_id

  UNION

  SELECT Client.Id, Client.Name, Manufacturer.Id, Manufacturer.Name
  FROM InstructionTemplate
  INNER JOIN Client on Client.Id = InstructionTemplate.Client_Id
  INNER JOIN Manufacturer on Manufacturer.Id = InstructionTemplate.Manufacturer_id
) a
GROUP BY Client_Id, Client_Name, Manufacturer_Id, Manufacturer_Name;

不幸的是，将这样的查询转换为NHibernate的查询API之一是不可能的，因为NHibernate不支持UNION语句*。在NHibernate的错误跟踪器中查看此question和功能请求NH-2710。

*使用union-subclass时除外。有关详细信息，请参阅docs

我能看到的唯一选择是

执行SQL查询并将其映射到DTO

public class InstructionTemplateInfo
{
  public int Client_Id { get; set; }
  public string Client_Name { get; set; }
  public int Manufacturer_Id { get; set; }
  public string Manufacturer_Name { get; set; }
}

然后

var result = session
       .CreateSQLQuery(theSQLQueryString)
       .SetResultTransformer(Transformers.AliasToBean<InstructionTemplateInfo>())
       .List<InstructionTemplateInfo>();

在数据库中创建一个视图，并将其映射为普通实体。

如果DBMS支持多个结果集，例如SQL Server，您可以编写两个查询，但将它们标记为Future，然后在代码中合并两个结果集，即

var resultSet1 = Session.QueryOver<ClientTaxEntity>(() => taxEntity)
           .JoinAlias(x => x.Client, () => client)
           .JoinAlias(x => x.Manufacturers, () => manufacturer)
           .SelectList(builder => builder
             .SelectGroup((() => client.Name).WithAlias(() => info.ClientName)
             .SelectGroup((() => client.Id).WithAlias(() => info.ClientId)
             .SelectGroup((() => manufacturer.Name).WithAlias(() => info.ManufacturerName)
             .SelectGroup((() => manufacturer.Id).WithAlias(() => info.ManufacturerId)
          .TransformUsing(Transformers.AliasToBean<InstructionTemplateInfo>())
          .Future<InstructionTemplateInfo>;

var resultSet2 = Session.QueryOver<InstructionTemplate>(() => taxEntity)
           .JoinAlias(x => x.Client, () => client)
           .JoinAlias(x => x.Manufacturers, () => manufacturer)
           .SelectList(builder => builder
             .SelectGroup((() => client.Name).WithAlias(() => info.ClientName)
             .SelectGroup((() => client.Id).WithAlias(() => info.ClientId)
             .SelectGroup((() => manufacturer.Name).WithAlias(() => info.ManufacturerName)
             .SelectGroup((() => manufacturer.Id).WithAlias(() => info.ManufacturerId)
          .TransformUsing(Transformers.AliasToBean<InstructionTemplateInfo>())
          .Future<InstructionTemplateInfo>;

var result = resultSet1.Concat(resultSet2 )
     .GroupBy(x=>x.ClientId+"|"+x.ManufacturerId)
     .Select(x=>x.First());

这种方法的优点是DBMS只会被击中一次。有关此功能的详细信息，请参阅Ayende's blog post。

NHibernate QueryOver - 无路径连接（或“反向”路径）

1 个答案: