android studio sqlite foreign key references

Android studio sqlite foreign key references how to#
Android studio sqlite foreign key references android#
Android studio sqlite foreign key references password#
Android studio sqlite foreign key references series#

+ '(Match_id integer primary key autoincrement, ' ' FOREIGN KEY(match_id) REFERENCES '+ matchTableName+'(Match_id),' + 'FOREIGN KEY(player_id) REFERENCES '+ playerTableName+'(Player_id),' +

+ '(Participant_id integer primary key autoincrement, ' + + '(Match_id integer primary key autoincrement, ' + MyDB.execSQL('CREATE TABLE IF NOT EXISTS '

Android studio sqlite foreign key references password#

'UserName VARCHAR, Password VARCHAR, Experience INTEGER, Rating INTEGER) ') + ' (Player_id integer primary key autoincrement, ' +

Android studio sqlite foreign key references how to#

I am trying to create the Match table so that it can reference two Match participants but I am unsure how to do this.Ĭode I have done to create tables myDB.execSQL('CREATE TABLE IF NOT EXISTS ' Then finally a Match participant table which will have an id, player_id (foreign key), match_id (foreign key) and a score which is an integer. I have a player table which contains an id, name password. Using the ForeingKey allows you to decide what should happen with the entity when the corresponding parent is deleted.I am trying to store match results in a database. = 'books',Įven though you cannot use direct relationships, Room still allows you to define ForeignKey constraints between entities. Let’s add some code! We will add Book entity. To reference multiple entities at the same time we need to create a POJO that contains each entity and write a query that will join corresponding tables.Įven though you cannot use direct relationships, Room still allows you to define Foreign Key constraints between entities. The Room comes across with something that mixes these two approaches. We can also use Eager loading where we lose all the performance gain, and we will load big amounts of useless data. We can use Lazy Loading that will allow our app to query faster, load fewer data and improve the performance - but we can struggle with querying on UI thread and risk the glitches. So, on the other hand instead of lazy loading we can use eager loading and load all necessary data earlier - but this will cause the overloading of the data and we will load something that isn’t needed in current point of the app. This will invoke another query to get the author’s name - on the main thread! This can end up with glitches in your app UI. Now if you try to set a text on the TextView and you need an authors name you will write something like this: textView.text = book.getAuthor().getName() In such construction and lazy loading, Book will use getAuthor() method to return the author - the first call of this method will query DB for the corresponding Author.

UI needs approximately ~16ms to calculate and draw an updated Activity layout - so if you add to this a lazy loading call for some entity field that can take ~5ms you can run of out time to draw an updated frame for Activity.įor example, let`s assume that we can add object reference class var id: Long,

Android studio sqlite foreign key references android#

Common ORMs allow you to use object references and thus ORMs implement lazy loading which was considered as potentially dangerous in Android apps. Working with Room relations is a bit tricky. Even though most object-relational mapping libraries allow entity objects to reference each other, Room explicitly forbids this. The Room doesn’t allow object referencesīecause SQLite is a relational database, you can specify relationships between objects. Part 2 can be found here - it was focused on entities and this part, I will show you how to add relations between tables/entities and how to query them properly.Īll sources can be found in related GitHub project.

Part 1 can be found here - it was focused on configuring the project and explaining the basic structures.

Android studio sqlite foreign key references series#

This article is the third and the last part of the three-part series that will smoothly introduce Room Persistence Library to you.