![]() ![]() unscoped SELECT books.* FROM books WHERE books.out_of_printįor every field (also known as an attribute) you define in your table,Īctive Record provides a finder method. If an update request is made with a lower value in the lock_version field than is currently in the lock_version column in the database, the update request will fail with an ActiveRecord::StaleObjectError. Each time the record is updated, Active Record increments the lock_version column. In order to use optimistic locking, the table needs to have a column called lock_version of type integer. An ActiveRecord::StaleObjectError exception is thrown if that has occurred and the update is ignored. It does this by checking whether another process has made changes to a record since it was opened. Optimistic locking allows multiple users to access the same record for edits, and assumes a minimum of conflicts with the data. Locking is helpful for preventing race conditions when updating records in the database and ensuring atomic updates.Īctive Record provides two locking mechanisms: save CopyĪs customer is explicitly set to be a readonly object, the above code will raise an ActiveRecord::ReadOnlyRecord exception when calling customer.save with an updated value of visits. Using the find method, you can retrieve the object corresponding to the specified primary key that matches any supplied options. Run after_find and then after_initialize callbacks, if any.Īctive Record provides several different ways of retrieving a single object.Instantiate the equivalent Ruby object of the appropriate model for every resulting row. ![]() Fire the SQL query and retrieve the corresponding results from the database.Convert the supplied options to an equivalent SQL query.The primary operation of Model.find(options) can be summarized as: Methods that find a single entity, such as find and first, return a single instance of the model. Each finder method allows you to pass arguments into it to perform certain queries on your database without writing raw SQL.įinder methods that return a collection, such as where and group, return an instance of ActiveRecord::Relation. To retrieve objects from the database, Active Record provides several finder methods. Retrieving Specific Data from Multiple TablesĬlass Supplier Retrieving Filtered Data from Multiple Tables.What is the Active Record Query Interface?. ![]()
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