Database tables:
Tutor( {PK}tutorId, name )
Module( {PK}moduleId, name, {FK}tutorId )
Relationship Tutor -> Module (OneToMany)
Questions:
If you create the domain model
classes with JPA annotations, the
corresponding database tables are
auto-created with the same columns as the annotated fields of the class?
Do you create the database first
and then the JPA classes with the
same fields as the database table
columns?
How do you model foreign key constraints with JPA
(1) and (2) are depended on your situation. you can create domain model class first and it will generate table and columns which are the similar to the fields. In addition, you can establish a database first (it is easy to design and have better view of the whole database.), then map the tables to your domain class.
about (3) you can try this link
Related
I use hibernate as the framework for springboot CUBA operations. But I have a problem, our workout information and recipe information are coming from external API. This means that I only need to store the recipe and workout ids in the database. The database structure is as follows.
DB sturucture
As the data is provided by the API, we have not created corresponding entity tables for workouts and recipes. But then the problem arises. What should be done with the join table in this case. I mean the premise of #manytomany is that two entity tables are needed, and we only have entity tables for users. Even if we use a joint primary key, there is still a need to add user_id as a foreign key in the joint primary key. How can we mark user_id as a foreign key without a workout or recipe entity table?
Your question is quite confusing but I'll try to provide an answer for what I understood.
If the data is completely external, you can map an element collection consisting of ids only:
#Entity
public class User {
// other fields
#ElementCollection
#CollectionTable(name = "recipse_user")
Set<Long> recipeIds;
#ElementCollection
#CollectionTable(name = "workout_user")
Set<Long> workoutIds;
}
Since I designed my db, I came out with a self related model in my entity relational diagram. I have the entity country and the relation that go from country to the same country that is called passyingby and it has its own attributes transfer description.
So I would have tables:
country(nameCountry), passyingby(nameCountry1,nameCountry2,transfer_description).
How can I manage this in Laravel considering also the unique values of passyingby rows? I have created a migration to create the table country and its related model.
I have mapped two different POJO classes into single mysql table .Now when I inserting data Into that table it stores data in two dirrent rows under different Id , while i want to store both class's data into same row under same Id ,I have used a common Id(primary key auto_increment) for mapping both POJO classes.
I know that parent-child relationship can be mapped into single table but mapping two different classes into single table that's something new. please add your mapping to see how you are doing it.
One way i think of is using a composition
http://www.dzone.com/tutorials/java/hibernate/hibernate-example/hibernate-mapping-component-1.html
I had a pure junction table (to represent a many-to-many relationship) in my database. That is, a table with only two columns, each of them being a foreign-key, and them together composing the primary-key.
EF hid that complexity from me by not mapping this table to an entity, as expected; it was mapped as an Association.
Then I added a new column to this junction table in my database, and went on to Update Model From Database in the EDMX. But the table remained as an Association, not turning into an Entity with 3 properties.
What am I missing?
The thing is you need to delete the association first. Go to Model Browser > Your Model > Associations, find and delete the association. Then you can update the model and the table will show up as an entity.
I'm using VS 2010, Entity Framework 4.3 and MySql.Data.Entity v6.3.5 to work with a MySQL DB with a couple dozen tables. I use the ADO.NET DbContext Generator.
Everything works well enough other than two tables don't get Entities created for them. Both have a similar structure in that they have a composite key composed of foreign keys to other tables. So, one is a region_flavor table that maps the (ice cream) flavors assigned to a particular sales region. It looks like so
region_flavor
-------------
RegionId INT(10) PK NN
Flavor VARCHAR(64) PK NN
RegionId is a FK to the regions table and Flavor is a FK to the ice_cream table.
There's another table with essentially the same situation.
When I do an "Update from Database", I see that there is, in the Model Browser, the table region_flavor listed under my IceCreamModel.Store\Tables / Views folder. But under my IceCreamModel\Entity Types folder there's no Entity Type.
I don't receive any .edmx errors when I do the update from the DB.
Perhaps I'm missing something here. Ideas?
I can post more info if that's helpful.
It is normal behavior. This is junction table used to model many-to-many relation in database. If it doesn't contain any additional column EF doesn't need to map it to entity because many-to-many relation is modeled directly and translated to table rows internally by EF.