What exactly is an active record? I hear this term used in Ruby post and nhibernate.
Active record was initially a design pattern which involved wrapping database table operations in a class.
In a Rails context, however, it is also the proper name of a particular software component which implements the design pattern in Ruby for object-relational mapping, and the name of its associated module.
Active record is a design pattern where you map each table to a class. This means that each object created from this class represents a row in the table.
http://martinfowler.com/eaaCatalog/activeRecord.html
http://en.wikipedia.org/wiki/Active_record_pattern
It s a Design Pattern.
http://martinfowler.com/eaaCatalog/activeRecord.html
Related
Was it Taylor Otwell himself or some company or someone else?
I am just curious and wanted to know. There is nothing to it in first page of google search so I posted the question here.
Maybe this will be down voted immediately. In that case I will delete it.
In software engineering, the active record pattern is an architectural pattern found in software that stores in-memory object data in relational databases. It was named by Martin Fowler in his 2003 book Patterns of Enterprise Application Architecture.1 The interface of an object conforming to this pattern would include functions such as Insert, Update, and Delete, plus properties that correspond more or less directly to the columns in the underlying database table.
The active record pattern is an approach to accessing data in a database. A database table or view is wrapped into a class. Thus, an object instance is tied to a single row in the table. After creation of an object, a new row is added to the table upon save. Any object loaded gets its information from the database. When an object is updated, the corresponding row in the table is also updated. The wrapper class implements accessor methods or properties for each column in the table or view.
This pattern is commonly used by object persistence tools and in object-relational mapping (ORM). Typically, foreign key relationships will be exposed as an object instance of the appropriate type via a property.
Resource: Laravel Up And Running book from Matt Stauffer
then you can find it even here.
So Taylor only used this pattern to implement in Laravel framework even though many they consider that as a weak part of Laravel.
Let's say we are structuring an application with MVC (also, Stores/Services). SQL is used as the persistence mechanism. And memory efficiency is a major concern.
Obviously, we should take advantage of SQL queries and only ask for fields of our Model in theory object when they are needed.
For example, an mobile app may need to display a list of title for articles, while the body of the article doesn't get displayed until user taps on a specific title. In this case, we ask SQL for just the titles first.
The question is, what should the model object look like?
The solutions I can think of are:
Enhance the model with some states that indicate which fields are populated. This could also be archived by using nil/NULL/None values on unpopulated fields of the model object.
Split the theoretical model to multiple classes. Following the previous example, we could have an Article class and an ArticleDetail class, with a one-to-one relation.
Forget the Store object, let each model object lazy evaluate it's costly fields. The model would have to know about its persistence mechanism.
This should be a common problem. How do the ORM in your favorite frameworks/libraries resolve it? Any best practices?
I'm having a few tables on SQL Server, which have similar structure - int Id and string Value.
This tables linked to main table via foreign key, so I'm wrote a bit of logic for mapping a string values to id's in models in MVC Razor. This feature requires that models used as dictionary implement simple IKeyValue interface with Id and Value, but after updating model from database I can loose interface implementation from models and must write it again.
Any way to automate this?
Are you modifying the auto-generated file? If so, you should not do this, for the exact reason you describe in your question -- it will get overwritten.
All of the classes in the generated file should be partial. You can take advantage of this by creating another class (in a different file, but in the same project), make sure it has the same declaration (and namespace), and have it implement the interface. This way the class will implement the interface, but will not be overwritten the next time you refresh the schema from the database.
I am wondering how the models in code ignitor are suposed to be used.
Lets say I have a couple of tables in menu items database, and I want to query information for each table in different controllers. Do I make different model classes for each of the tables and layout the functions within them?
Thanks!
Models should contain all the functionality for retrieving and inserting data into your database. A controller will load a model:
$this->load->model('model_name');
The controller then fetches any data needed by the view through the abstract functions defined in your model.
It would be best to create a different model for each table although its is not essential.
You should read up about the MVC design pattern, it is used by codeigniter and many other frameworks because it is efficient and allows code reuse. More info about models can be found in the Codeigniter docs:
http://codeigniter.com/user_guide/general/models.html
CodeIgniter is flexible, and leaves this decision up to you. The user's guide does not say one way or the other how you should organize your code.
That said, to keep your code clean and easy to maintain I would recommend an approach where you try to limit each model to dealing with an individual table, or at least a single database entity. You certainly want to avoid having a single model to handle all of your database tables.
For my taste, CodeIgniter is too flexible here - I'd rather call it vague. A CI "model" has no spec, no interface, it can be things as different as:
An entity domain object, where each instance represents basically a record of a table. Sometimes it's an "anemic" domain object, each property maps directly to a DB column, little behaviour and little or no understanding of objects relationships and "graphs" (say, foreign keys in the DB are just integer ids in PHP). Or it can also be a "rich (or true) domain object", with all the business intelligence, and also knows about relations: say instead of $person->getAccountId() (returns int) we have $person->getAccount(); perhaps also knows how to persist itself (and perhaps also the full graph or related object - perhaps some notion of "dirtiness").
A service object, related to objects persistence and/or general DB querying: be a DataMapper, a DAO, etc. In this case we have typically one single instance (singleton) of the object (little or no state), typically one per DB table or per domain class.
When you read, in CI docs or forums, about , say, the Person model you can never know what kind of patter we are dealing with. Worse: frequently it's a ungly mix of those fundamentally different patterns.
This informality/vagueness is not specific to CI, rather to PHP frameworks, in my experience.
Coming from a Java/Hibernate environment, I can map some columns within a table to be a "component" that is belongs to a parent class. For example an User object contains a Preference object, which actually mapped all the attributes into one table in the database.
Is there anything similar in DataMapper? or other database interfacing library?
DataMapper currently doesn't support this feature, but it's on the roadmap and is referred to as "embedded value". ActiveRecord supports defining embedded values already.
As long as DataMapper has no builtin support for embedded values, they can be "faked" by following the pattern outlined in https://gist.github.com/873428