And the validation raises an error prior to your database in this case.ĭefines if the column gets included if you call an insert statement with your JPA provider. Most os the time you specify the same thing within the database too however it is good to let your fellow developers know that they should not enable a null for this field. If you generate your tables outside of your persistence api (for example with Liquibase) then you do not need this parameter. It is a shourtcut for the uniqueConstraints. This can change if you plan to make your columns unse an uderscore (“_”) where you use camleCase in your Java class. Parameterĭefaults to the same column name of the variable. Here you can define your unique constraints you’d like to append to this is more interesting because this you use more often to describe some valuable information for your columns: for example different names as in the Java class. The uniqueConstraints get important if you generate your database tables from your Java classes. This comes handy if your database table has another name than your Java class (for example you need the tables have a specific prefix or your table/class name would be a keyword in Java or in your database.įor granularity you can specify catalog and schema of the table but I’ve never seen scenarios in my projects where we needed this. However sometimes you need to use at least the column property of Table: this tells the implementing JPA library which database table to look at if handling this type of objects. toDTO has some optional parameters, which default to an empty String or an empty array (uniqueConstraints). I’ve seen some projects where you had to convert every entity into a DTO and it was most of the time just a 1:1 copy in the entity (with. Otherwise just give away your entities over the borders. in a GUI) or want a subset of data collected from a couple of entities. However if you’d like my opinion: you only need DTOs if you need some custom representation of an entity (i.e. It is philosophy, every aspect has its own pros and cons. And another reason for the “WHY”: sometimes there are restrictions not to reach your entities outside of your module border - and with the Entity at the end you can see that you should not access this object but get a DTO instead. The answer could be that this is defined in the project: “Every Entiy’s class name has to end with Entity.” This is a good enough reason - and eventually you can have a Checkstyle which gives you a nice yellow warning if you miss this part. What you can ask is “Why do you specify Entity in the class name because it is obvious from the annotation?”. This allows that you can query CustomerEntity objects from the database referencing them as Customer - saving the Entity part in your queries. Let’s examine this through a simple = " Customer" )Īs you can see above the CustomerEntity class is an entity with the name Customer. If you not set it, the name will be the name of the Java class. Entity, Table, Columnįirst of all let’s take a look at the general annotations you use with your has only one optional parameter and it is name. The only time I needed some Hibernate specific annotation was JodaTime - but this is another story. But as I mentioned above I try to stick strictly to the usage of common javax.persistence annotations. So in this article I’ll create a little cheat sheet for myself of the annotations’ attributes and defaults and eventually you can benefit from it too.Īs mentioned in the preface I use Hibernate’s implementation of javax.persistence because they have comments and easily downloadable sources into Eclipse. Now I encountered a project where we use JPA2.0 (implementation by Hibernate but this is mostly out of the question) and I need some information about the used annotations - and especially their optional parameters and default values. I learned in my years as a software developer that I learn things then better if I try them, create a short application with them.
0 Comments
Leave a Reply. |