我不能在代码中使用任何ID

Question

I was always taught to use IDs in my code to refer to records into the database.

But let's take the case we have same roles in the table Role. Now I want to query only the records related to the role Player:

ID    ROLE
1     Admin
2     Organizer
3     Player

I don't know in my code the ID of Player, but I want to retrieve all the players, so with Hibernate I wrote:

String queryString = "from User u where u.role.role = ?";
Query queryObject = getSession().createQuery(queryString);
queryObject.setParameter(0, "player");
return queryObject.list();

As you can see I wrote "player" in the code. I think this is not the best way and I should use an ID instead. But I don't know the ID and it may change depending on the server on which I run the application. A second problem with my solution is that "player" can be capitalized into the database and this may be changed over time.

So, what should be the solution to all these problems? Is there any way to use the ID instead? Or any other way to improve this code?

Answer 1

In this case it seems that role should be an enum and your query would look something like:

queryObject.setParameter(0, Role.PLAYER);

Also, you might take a look at the criteria API which will help you create more type-safe queries that are more robust vs. refactoring.

Answer 2

You can do using create a mapping table like ,

UserRoleMapping ID - Incremental, UserId - Refers to user table, RoleId - Refers to role table

As one user can have more than one role so it will satisfy that thing too. to Get the roles using query

select role.id from userrolemapping urm innerjoin on user u.id = urm.id where u.id = ?

Answer 3

You should create a enum class like this.

public enum Role {

Admin(1),
Organizer(2),
Player(3);

}

And change your code to

String queryString = "from User u where u.id= ?";
Query queryObject = getSession().createQuery(queryString);
queryObject .setParameter(0, Role.PLAYER);
return queryObject.list();

Answer 4

using IDs or string/vachar etc. lookup is all dependent on the data that you have in the database. Some organization keep the id static and some keep the name/description static. So, make sure you have good understanding of your DB data and what will stay static . However, if the role is static you can use HQL ignore case like the example I provided for you below (I'm not adding information about the ID static path because others have already provided information about it for and don't want to duplicate it ). --note you can take the percentages out if you only want "player"

String queryString = "from User u where lower( u.role.role )  like lower('%"+ ? +"%')";
Query queryObject = getSession().createQuery(queryString);
queryObject.setParameter(0, "player");
return queryObject.list();