如何使用ServiceStack OrmLite两次两次将LeftJoin加入同一张表? [英] How to LeftJoin to the same table twice using ServiceStack OrmLite?

问题描述

我的表格结构如下:

table Tenant: Id[PK], etc
table Contact: Id[PK], FirstName, LastName etc
table Sale: Id[PK], TenantId[FK], SellerId[FK], BuyerId[FK], etc

SellerId is a FK to Contact.Id
BuyerId is a FK to Contact.Id
TenantId is a FK to Tenant.Id

我想使用OrmLite生成类似于以下内容的SQL:

I want to use OrmLite to generate SQL similar to below:

select  sale.*
    ,   buyer.FirstName 'BuyerFirstName'
    ,   buyer.LastName 'BuyerLastName'
    ,   seller.FirstName 'SellerFirstName'
    ,   seller.LastName 'SellerLastName'
from    sale
    left join
        contact seller
    on  sale.SellerId = seller.Id
    left join
        contact buyer
    on  sale.BuyerId = buyer.Id
where   tenantId = 'guid' -- this is being filtered at a global level

因为我想要一个强类型的全局过滤器，以按tenantId(在数据库方面)过滤出结果，所以我的代码如下所示

Because I want to have a strongly typed global filter to filter out result by tenantId (on database side) I have code looks like below

public List<TOut> Exec<TIn, TOut>(SqlExpression<TIn> exp) where TIn : IHaveTenantId
{
    exp.Where(x => x.TenantId == _tenantId);
    return _conn.Select<TOut>(exp);
}

销售的主题如下:

public class Sale : IHaveTenantId
{
    public Guid Id { get; set; }

    [ForeignKey(typeof(Contact), OnDelete = "CASCADE")]
    public Guid BuyerId { get; set; }

    [ForeignKey(typeof(Contact), OnDelete = "CASCADE")]
    public Guid SellerId { get; set; }

    //etc
}

我正尝试使用如下所示的强类型LeftJoin语法:

And I'm trying to use strongly typed LeftJoin syntax like below:

public class SaleView
{
    public Guid Id { get; set; }
    public string BuyerFirstName { get; set; }
    public string SellerLastName { get; set; }
    //etc
}

var result = Exec<SaleView, Sale>(_conn
    .From<Sale>()
    .LeftJoin<Contact>((sale, seller) => sale.SellerId == seller.Id)
    .LeftJoin<Contact>((sale, buyer) => sale.BuyerId == buyer.Id));

我无法弄清楚如何多次联接同一张表，并且每次联接都具有别名(例如，左联接联系人为卖方"，因此我可以选择"seller.FirstName"，"buyer.FirstName")，但我却没有想要使用参数化的原始sql.

I couldn't figure out how to join the same table multiple times and have an alias per join (e.g. left join contact as 'seller', hence I can select seller.FirstName, buyer.FirstName) and I don't want to use parameterised raw sql.

OrmLite完全可以吗?

Is this possible at all with OrmLite?

推荐答案

对

在v4.0.62之前，您可以继续使用带有自定义SQL的Typed SqlExpression，例如:

Prior to v4.0.62 you can continue to use a Typed SqlExpression with custom SQL for this, e.g:

var q = db.From<Sale>()
    .CustomJoin("LEFT JOIN Contact seller ON (Sale.SellerId = seller.Id)")
    .CustomJoin("LEFT JOIN Contact buyer ON (Sale.BuyerId = buyer.Id)")
    .Select(@"Sale.*
        , buyer.FirstName AS BuyerFirstName
        , buyer.LastName AS BuyerLastName
        , seller.FirstName AS SellerFirstName
        , seller.LastName AS SellerLastName");

这样做的好处是它仍然保留Typed API，您可以在其中添加其他过滤器，例如全局TenantId过滤器，例如:

The benefit of which is that it still leaves a Typed API where you can add additional filters like a global TenantId filter, e.g:

q.Where(x => x.TenantId == tenantId);

然后使用以下命令将其投影到您的自定义POCO中:

And then project it into your Custom POCO with:

var sales = db.Select<SaleView>(q);

v4.0.37 + 中提供了新的CustomJoin API，该API 现在在MyGet上可用.

The new CustomJoin API is available from v4.0.37+ that's now available on MyGet.

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