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How to embed multiple entities in Android Room Database

Introduction:

In the realm of Android app development, Room Database stands as a robust solution for data persistence. However, as developers, we often grapple with the challenge of efficiently accessing one-to-one relationships between entities. This article aims to unravel the complexities surrounding the integration of multiple entities within the Android Room Database, offering a cleaner and more accessible solution.

The Dilemma:

Consider a scenario where your project involves entities for addresses, owners, and sites. Both owners and sites are associated with an address, and each site has an owner. The question arises: Is it possible to navigate through these relationships seamlessly, for instance, accessing site.owner.address.l1?

The Existing Approach:

The initial attempt involves exploring the @Relation annotation. However, it poses a limitation by returning a list, which may not be the most optimal solution. An alternative approach is to employ multiple POJOs (Plain Old Java Objects) to establish relationships, but this method may not be the most elegant or efficient.

The Solution: Building Relationships

The Android Room Database allows us to create relationships between entities, providing a more cohesive and straightforward approach. Let’s delve into the solution by refining the existing entities and incorporating relationships.

@Entity(tableName="addresses") data class Address( @PrimaryKey @ColumnInfo(name="address_id") val id: Int, @ColumnInfo(name="address_l1") val l1: String ) @Entity(tablename="owners") data class Owner( @PrimaryKey @ColumnInfo(name="owner_id") val id: Int, @ColumnInfo(name="owner_name") val name: String, @ColumnInfo(name="owner_address") @Entity val address: Address ) @Entity(tableName="sites") data class Site( @PrimaryKey @ColumnInfo(name="site_id") val id: Int, @ColumnInfo(name="site_owner") @Embedded val owner: Owner, @ColumnInfo(name="site_address") @Embedded val address: Address )

Explanation:

By refining the entity structure, we establish direct relationships between Address, Owner, and Site entities. Now, each Site contains an Address and an Owner, where the Owner, in turn, includes its associated Address. Both the ‘sites’ and ‘owners’ tables will now have Address columns, simplifying the navigation through relationships.

Conclusion:

Mastering Android Room Database relationships involves thoughtful entity design and utilization of Room’s features. By building relationships between entities, you create a more intuitive and efficient structure for accessing interconnected data. This solution not only enhances code clarity but also streamlines the retrieval of information in a more organized manner. Embrace the power of relationships in Room Database to elevate your Android app development experience.