What is the difference between IS -A relationship and HAS-A relationship in Java? - Stack Overflow
The "has-many-through" relationship provides a convenient shortcut for accessing distant relations via an intermediate. This article contains: IS-A relationship in OOP (Inheritance), Has-A relationship ( Association), Different type of Association: Aggregation and. Classifier in UML can have zero, one or many generalization relationships to more general classifiers. In OOAD multiple inheritance refers to the ability of a class.
Association Wrote between Professor and Book with association ends author and textbook.
Association End Association end is a connection between the line depicting an association and the icon depicting the connected classifier. Name of the association end may be placed near the end of the line. The association end name is commonly referred to as role name but it is not defined as such in the UML 2.
The role name is optional and suppressible. Professor "playing the role" of author is associated with textbook end typed as Book. The idea of the role is that the same classifier can play the same or different roles in other associations.
For example, Professor could be an author of some Books or an editor. Association end could be owned either by end classifier, or association itself Association ends of associations with more than two ends must be owned by the association. Ownership of association ends by an associated classifier may be indicated graphically by a small filled circle aka dot.
How to use a 'has a' relationship : Member Variable « Class « C# / CSharp Tutorial
The dot is drawn at the point where line meets the classifier. It could be interpreted as showing that the model includes a property of the type represented by the classifier touched by the dot.
This property is owned by the classifier at the other end. Association end query is owned by classifier QueryBuilder and association end qbuilder is owned by association Builds itself The "ownership" dot may be used in combination with the other graphic line-path notations for properties of associations and association ends. These include aggregation type and navigability. UML standard does not mandate the use of explicit end-ownership notation, but defines a notation which shall apply in models where such use is elected.
Dynamic Properties If you do not need to add additional constraints to an Eloquent relationship query, you may access the relationship as if it were a property. For example, continuing to use our User and Post example models, we may access all of a user's posts like so: Because of this, developers often use eager loading to pre-load relationships they know will be accessed after loading the model.
Eager loading provides a significant reduction in SQL queries that must be executed to load a model's relations. Querying Relationship Existence When accessing the records for a model, you may wish to limit your results based on the existence of a relationship.
For example, imagine you want to retrieve all blog posts that have at least one comment. To do so, you may pass the name of the relationship to the has and orHas methods: For example, you may retrieve all posts that have at least one comment and vote: These methods allow you to add customized constraints to a relationship constraint, such as checking the content of a comment: For example, imagine you want to retrieve all blog posts that don't have any comments.
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To do so, you may pass the name of the relationship to the doesntHave and orDoesntHave methods: These methods allows you to add customized constraints to a relationship constraint, such as checking the content of a comment: For example, the following query will retrieve all posts with comments from authors that are not banned: This means the relationship data is not actually loaded until you first access the property.
However, Eloquent can "eager load" relationships at the time you query the parent model.
So, if we have 25 books, this loop would run 26 queries: Thankfully, we can use eager loading to reduce this operation to just 2 queries. When querying, you may specify which relationships should be eager loaded using the with method: Eager Loading Multiple Relationships Sometimes you may need to eager load several different relationships in a single operation.
To do so, just pass additional arguments to the with method: For example, let's eager load all of the book's authors and all of the author's personal contacts in one Eloquent statement: For this reason, Eloquent allows you to specify which columns of the relationship you would like to retrieve: Constraining Eager Loads Sometimes you may wish to eager load a relationship, but also specify additional query constraints for the eager loading query.
HAS-A relationship in Java
Of course, you may call other query builder methods to further customize the eager loading operation: For example, this may be useful if you need to dynamically decide whether to load related models: The array values should be Closure instances which receive the query instance: For example, perhaps you need to insert a new Comment for a Post model.
Instead, we called the comments method to obtain an instance of the relationship. If you need to save multiple related models, you may use the saveMany method: Again, the difference between save and create is that save accepts a full Eloquent model instance while create accepts a plain PHP array: You may use the createMany method to create multiple related models: Belongs To Relationships When updating a belongsTo relationship, you may use the associate method.
This method will set the foreign key on the child model: This method will set the relationship's foreign key to null: This pattern is often referred to as the Null Object pattern and can help remove conditional checks in your code. For example, let's imagine a user can have many roles and a role can have many users. To attach a role to a user by inserting a record in the intermediate table that joins the models, use the attach method: To remove a many-to-many relationship record, use the detach method.
The detach method will remove the appropriate record out of the intermediate table; however, both models will remain in the database: The sync method accepts an array of IDs to place on the intermediate table. Very few people apologize before they are asked to--or even before anyone notices they should. Responsibility is a key building block of a great relationship.
HAS-A relationship in Java
People who take the blame, who say they are sorry and explain why they are sorry, who don't try to push any of the blame back on the other person--those are people everyone wants in their lives, because they instantly turn a mistake into a bump in the road rather than a permanent roadblock.
Give consistently, receive occasionally. A great relationship is mutually beneficial. In business terms that means connecting with people who can be mentors, who can share information, who can help create other connections; in short, that means going into a relationship wanting something. The person who builds great relationships doesn't think about what she wants; she starts by thinking about what she can give. She sees giving as the best way to establish a real relationship and a lasting connection.
She approaches building relationships as if it's all about the other person and not about her, and in the process builds relationships with people who follow the same approach. In time they make real connections.
And in time they make real friends. Value the message by always valuing the messenger. When someone speaks from a position of position of power or authority or fame it's tempting to place greater emphasis on their input, advice, and ideas. We listen to Tony Hsieh. We listen to Norm Brodsky. We listen to Seth Godin. The guy who mows our lawn? Maybe we don't listen to him so much. Smart people strip away the framing that comes with the source--whether positive or negative--and consider the information, advice, or idea based solely on its merits.
People who build great relationships never automatically discount the message simply because they discount the messenger. They know good advice is good advice, regardless of where it comes from. And they know good people are good people, regardless of their perceived "status. I sometimes wear a Reading Football Club sweatshirt. The checkout clerk at the grocery store noticed it one day and said, "Oh, you're a Reading supporter? My team is Manchester United.