ORM = Object-Relational Mapping In an ORM, classes/objects in the application are mapped to database tables and operations for persistence, sometimes automagically. DAL = Data-Access Layer In a DAL, database operations are hidden behind a code facade. An ORM is a kind of DAL, but not all DALs are ORMs.
Use the serial type for automatically incrementing unique ids. If you plan to have more than two billion entries, use bigserial. serial is the PostgresSQL equivalent of MySQL’s AUTO_INCREMENT. PostgresSQL Documentation: Numeric Types
Yes. Ensures that you don’t have an orphan (entry with no parent), and depending on usage, if you define a cascading delete, when a parent is deleted, all its children will also be deleted. Disadvantage would be a slight performance hit just like any other foreign key.
Which table is the child in the relationship? Answer that, and you know which table needs the foreign key column, referencing the parent’s [typically] primary key. That’s for a one-to-many relationship… A many-to-many would require you to add a third table, using the keys from both of the two tables as it’s primary key.
A schema is a namespace – a logical thing. It is used to organize the names of database objects. It has nothing to do with the way the data is stored. A tablespace is a physical thing. It’s a container for data and has nothing to do with the logical organization of the database objects. … Read more
I’ve also been looking for a single-page “quick reference” PDF for ERD relationship symbols (i.e. “Crows Feet”). I haven’t found anything I’ve liked, so I created this. I’ve posted the Full Page, Printable PDF on my blog. Hope this helps!
If you are looking for a way to create a data model to communicate your design, there are no tools out there specifically created to model json-structured data. However, you could use UML tools or XML design tools to create your models. I’ve been less than satisfied with both methods, but it’s all I have … Read more
I’m not a specialist but the read/write master database and read-only slaves pattern is a “common” pattern, especially for big applications doing mostly read accesses or data warehouses: it allows to scale (you add more read-only slaves if required) it allows to tune the databases differently (for either efficient reads or efficient writes) What would … Read more
As Forum has many topics, and a topic belongs to one and only Forum, you probably want to go with a Forum type attribute annotated with @ManyToOne: @ManyToOne @JoinColumn(name = “forumId”) private Forum forum; See more: ManyToOne and JPA mapping
Wow I just wrote a big post and SO choked and hung on it, and when I hit my back button to resubmit, the markup editor was empty. aaargh. So here I go again… Regarding Stack Overflow, it turns out that they use SQL server 2005 full text search. Regarding the OS projects recommended by … Read more