链式模型关联的自定义方法或关联

Question

我有三个模型：User、Product 和 Transaction。

以下是关联：

app/models/transaction.rb

# A transaction has a `current` boolean that is true when the transaction is currently happening, and nil else.

belongs_to :seeker, class_name: "User", foreign_key: "seeker_id"
belongs_to :product  

app/models/user.rb

has_many :owned_products, class_name: "Product",
                          foreign_key: "owner_id",
                          dependent: :destroy
has_many :transactions, foreign_key: "seeker_id",
                        dependent: :destroy
has_many :requested_products, through: :transactions, source: :product
has_many :active_transactions, -> { where current: true },
                               class_name: 'Transaction',
                               foreign_key: "seeker_id"
has_many :borrowed_products, through: :active_transactions, source: :product

app/models/product.rb

belongs_to :owner, class_name: "User",
                   foreign_key: "owner_id"
has_many :transactions, dependent: :destroy
has_many :seekers, through: :transactions,
                     source: :seeker  
has_one :active_transaction, -> { where current: true },
                             class_name: 'Transaction'
has_one :borrower, through: :active_transaction,
                            source: :seeker

我想创建一个允许我执行以下操作的方法：

user.owned_products.available # returns every product owned by the user that has a transaction with current:true.
user.owned_products.lended # returns every product owned by the user that has no transaction with current.true

这可能吗？如果没有，我会做一个像user.available_products 和user.lended_products 这样的关联链接，但我不知道怎么做，因为我必须使用两个模型的条件才能在第三个模型中建立关联，如下所示：

app/models/user.rb

has_many :available_products, -> { where borrower: nil },
                              class_name: "Product",
                              foreign_key: "owner_id"

我收到此错误消息：

ActionView::Template::Error:
   SQLite3::SQLException: no such column: products.borrower: SELECT COUNT(*) FROM "products"  WHERE "products"."owner_id" = ? AND "products"."borrower" IS NULL

有什么提示吗？

Answer 1

创建范围

scope :available, where(:current => true).joins(:transactions)

现在你可以说

user.owned_products.available

这未经测试。但这会让你知道如何继续前进。

Here 是作用域的参考。