具有多个表、左外连接和 where 子句的 LINQ 查询

Question

我需要将此 SQL 查询转换为 C# 中的 LINQ。如果您能提供任何帮助或指导，我将不胜感激。（我正在使用 entity framework 6）。

SELECT f.FacId
  ,sli.SitLocIntId
  ,ei.EnvIntId
  ,p.PhoId
FROM Fac AS f
join SitLocInt AS sli on f.FacId = sli.FacId
join EnvInt AS ei on sli.EnvIntId = ei.EnvIntId
join EnvIntTyp AS eit on ei.EnvIntTypId = eit.EnvIntTypId
left outer join Aff AS a on ei.EnvIntId = a.EnvIntId
left outer join AffCon AS ac on a.AffId = ac.AffId
left outer join Con AS c on ac.ConId = c.ConId
left outer join Pho AS p on c.ConId = p.ConId
WHERE EnvIntTyp = 'Fleet'

我一直在研究组连接语法，但是有这么多 tables，很多左外连接和一个 where 子句，我没有取得太大进展。到目前为止我有

    var testQuery =
        from f in _CEMDbContext.setFac
        join sli in _CEMDbContext.setSitLocInt on f.FacId equals sli.FacId
        join ei in _CEMDbContext.setEnvInt on sli.EnvIntId equals ei.EnvIntId
        join eit in _CEMDbContext.setEnvIntTyp on ei.EnvIntTypId equals eit.EnvIntTypId into eiGroup
        from item in eiGroup.DefaultIfEmpty().Where(e => e.EnvIntTyp == "Fleet")
        select new BusinessParticipant
        {
            fac = f,
            sitLocInt = sli,
            envInt = ei,
            // pho = p, // not working... Phone number from table Pho.
        }; 
    var TestList = testQuery.ToList();

正在获取 EnvIntTyp "Fleet" 及其所有相关数据，包括 Fac、SitLocInt 和 EnvInt。但是当我试图从 table Pho 中获取可能存在也可能不存在的 phone 号码时，我运行遇到了麻烦。有没有一种很好的方法可以将所有左外连接链接在一起？感谢您的建议或指导！

编辑我不仅需要我在 SQL 查询中写的 ID，还需要整个对象。另外，我应该提到 EnvIntTyp 是同名 table 的成员。

编辑 2 以下是（部分）相关实体。 Fac 是 Facility 的缩写。 SitLocInt 是 SiteLocationInterest 的缩写。 EnvInt 代表环境利益。 Aff 代表隶属关系。 Con 是联系方式。河粉适用于 Phone.

public partial class Facility
{
    public Facility()
    {
        this.SiteLocationInterests = new List<SiteLocationInterest>();
    }

    public int FacilityId { get; set; }
    public string FacilityIdentifier { get; set; }
    public string FacilityName { get; set; }
    public int SiteTypeId { get; set; }
    public string FacilityDescription { get; set; }
    [ForeignKey("GeographicFeature")]
    public Nullable<int> GeographicFeatureId { get; set; }
    [Display(Name = "resAddress", ResourceType = typeof(CEMResource))]
    public string AddressLine1 { get; set; }
    [Display(Name = "resAddressLine2", ResourceType = typeof(CEMResource))]
    public string AddressLine2 { get; set; }
    public string City { get; set; }
    [Display(Name = "resState", ResourceType = typeof(CEMResource))]
    public string StateCode { get; set; }
    [Display(Name = "resZip", ResourceType = typeof(CEMResource))]
    public string AddressPostalCode { get; set; }
    public string CountyName { get; set; }
    public virtual GeographicFeature GeographicFeature { get; set; }
    public virtual ICollection<SiteLocationInterest> SiteLocationInterests { get; set; }
}

public partial class SiteLocationInterest
{
    public int SiteLocationInterestId { get; set; }
    [ForeignKey("Facility")]
    public Nullable<int> FacilityId { get; set; }
    [ForeignKey("EnvironmentalInterest")]
    public Nullable<int> EnvironmentalInterestId { get; set; }
    public Nullable<int> EventId { get; set; }
    [ForeignKey("GeographicFeature")]
    public Nullable<int> GeographicFeatureId { get; set; }
    public System.DateTime CreateDate { get; set; }
    public string CreateBy { get; set; }
    public System.DateTime LastUpdateDate { get; set; }
    public string LastUpdateBy { get; set; }
    public virtual EnvironmentalInterest EnvironmentalInterest { get; set; }
    public virtual Facility Facility { get; set; }
    public virtual GeographicFeature GeographicFeature { get; set; }
}

public partial class EnvironmentalInterest
{
    public EnvironmentalInterest()
    {
        this.Affiliations = new List<Affiliation>();
        this.SiteLocationInterests = new List<SiteLocationInterest>();
    }

    public int EnvironmentalInterestId { get; set; }
    public string EnvironmentalInterestIdentifier { get; set; }
    public string EnvironmentalInterestFacilityIdentifier { get; set; }
    public string FacilityIdentifier { get; set; }
    public string EnvironmentalInterestName { get; set; }
    [ForeignKey("EnvironmentalInterestType")]
    public int EnvironmentalInterestTypeId { get; set; }
    public Nullable<int> EnvironmentalInterestSubTypeId { get; set; }
    public string EnvironmentalInterestDescription { get; set; }
    public virtual ICollection<Affiliation> Affiliations { get; set; }
    public virtual EnvironmentalInterestType EnvironmentalInterestType { get; set; }
    public virtual ICollection<SiteLocationInterest> SiteLocationInterests { get; set; }
}

public partial class Affiliation
{
    public Affiliation()
    {
        this.AffiliationContacts = new List<AffiliationContact>();
    }

    public int AffiliationId { get; set; }
    public string AffiliationIdentifier { get; set; }
    public string AffiliationName { get; set; }
    [ForeignKey("Entity")]
    public Nullable<int> EntityId { get; set; }
    [ForeignKey("EnvironmentalInterest")]
    public Nullable<int> EnvironmentalInterestId { get; set; }
    public int AffiliationTypeId { get; set; }
    public int StatusTypeId { get; set; }
    public virtual EnvironmentalInterest EnvironmentalInterest { get; set; }
    public virtual ICollection<AffiliationContact> AffiliationContacts { get; set; }
}

public partial class AffiliationContact
{
    public int AffiliationContactId { get; set; }
    public int AffiliationId { get; set; }
    public int ContactId { get; set; }
    public virtual Affiliation Affiliation { get; set; }
    public virtual Contact Contact { get; set; }
}

public partial class Contact
{
    public Contact()
    {
        this.AffiliationContacts = new List<AffiliationContact>();
        this.Phones = new List<Phone>();
    }

    public int ContactId { get; set; }
    public string ContactIdentifier { get; set; }
    public int EntityId { get; set; }
    public Nullable<int> MailAddressId { get; set; }
    public int ContactTypeId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string EmailAddress { get; set; }
    public virtual ICollection<AffiliationContact> AffiliationContacts { get; set; }
    public virtual Entity Entity { get; set; }
    public virtual ICollection<Phone> Phones { get; set; }
}

public partial class Phone
{
    public int PhoneId { get; set; }
    public int ContactId { get; set; }
    public int ContactTypeId { get; set; }
    public string PhoneNumber { get; set; }
    public string PhoneExtensionNumber { get; set; }
    public virtual Contact Contact { get; set; }
    public virtual ContactType ContactType { get; set; }
}

Answer 1

Northwnd db = new Northwnd(@"c:\northwnd.mdf");
IEnumerable<Customer> results = db.ExecuteQuery<Customer>
(@"SELECT c1.custid as CustomerID, c2.custName as ContactName
    FROM customer1 as c1, customer2 as c2
    WHERE c1.custid = c2.custid"
);

只要表格结果中的列名与您的实体 class 的列属性相匹配，LINQ to SQL 就会从任何 SQL 查询中创建您的对象。

您可以通过 Linq 在 C# 中执行本机 SQL 代码，因此您实际上根本不需要转换它。查看这篇 MSDN 文章：https://msdn.microsoft.com/en-us/library/bb399403(v=vs.110).aspx

Answer 2

让我们将问题简化为更容易理解的问题。这是一个简单的左连接：

SELECT As.AId, Bs.BId
FROM As
LEFT JOIN Bs ON As.AId = Bs.AId

在 LINQ 中：

from a in ctx.As
join b in ctx.Bs on a.AId equals b.AId into bgrp // group join -- put matching Bs
                                                 // into a group "bgrp".
from b in bgrp.DefaultIfEmpty()                  // from DefaultIfEmpty() -- if the group
                                                 // has any rows, return them. otherwise,
                                                 // return a single row with the
                                                 // entity's default value (null).
select new
{
    a.AId,
    b.BId
}

您可以通过重复链接多个左连接：

from a in ctx.As
join b in ctx.Bs on a.AId equals b.AId into bs
from b in bs.DefaultIfEmpty()
join c in ctx.Cs on b.BId equals c.BId into cs
from c in cs.DefaultIfEmpty()
select new
{
    a.AId,
    b.BId,
    c.CId
}

Answer 3

我是这样做的：

var bpQuery =
    from f in _CEMDbContext.setFac
    join sli in _CEMDbContext.setSitLocInt on f.FacId equals sli.FacId
    join ei in _CEMDbContext.setEnvInt on sli.EnvIntId equals ei.EnvIntId into eiGroup
    from eig in eiGroup.DefaultIfEmpty().Where(e => e.EnvIntTyp.EnvIntTyp == "Fleet")
    join a in _CEMDbContext.setAff on eig.EnvIntId equals a.EnvIntId into aGroup
    from ag in aGroup.DefaultIfEmpty()
    join ac in _CEMDbContext.setAffCon.DefaultIfEmpty() on ag.AffId equals ac.AffId into acGroup
    from acg in acGroup.DefaultIfEmpty()
    join c in _CEMDbContext.setCon.DefaultIfEmpty() on acg.ConId equals c.ConId into cGroup
    from cg in cGroup.DefaultIfEmpty()
    join p in _CEMDbContext.setPho.DefaultIfEmpty() on cg.ContactId equals p.ConId into pGroup
    from pg in pGroup.DefaultIfEmpty()
    select new BusinessParticipant
    {
        facility = f,
        sitLocInt = sli,
        envInt = eig,
        pho = pg,
    };                        

    BusinessParticipantList = bpQuery.ToList();

具有多个表、左外连接和 where 子句的 LINQ 查询

LINQ query with many tables, left outer joins, and where clause

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