Type ORM

Adding WHERE expression Adding a WHERE expression is as easy as: Which will produce: You can add AND into an existing WHERE expression: Which will produce the following SQL query: You can add OR into an existing WHERE expression: Which will produce the following SQL query: You can do an IN query with the WHERE expression: Which will produce the following SQL query: You can add a complex WHERE expression into an existing WHERE using Brackets…

Using parameters to escape data We used where("user.name = :name", { name: "Timber" }). What does { name: "Timber" } stand for? It’s a parameter we used to prevent SQL injection. We could have written: where("user.name = '" + name + "'), however this is not safe, as it opens the code to SQL injections. The safe way is…

 What is QueryBuilder QueryBuilder is one of the most powerful features of TypeORM – it allows you to build SQL queries using elegant and convenient syntax, execute them and get automatically transformed entities. Simple example of QueryBuilder: It builds the following SQL query: and returns you an instance of User: Important note when using the QueryBuilder When using the QueryBuilder, you…

It’s common practice assigning a repository instance to a globally exported variable, and use this variable across your app, for example: In order to extend UserRepository functionality you can use .extend method of Repository class:

Basic options All repository and manager .find* methods accept special options you can use to query data you need without using QueryBuilder: will execute following query: will execute following queries: will execute following query: Querying a column from an embedded entity should be done with respect to the hierarchy in which it was defined. Example: will execute following…

Many-to-many relations are a concept in database design and object-relational mapping (ORM) frameworks like TypeORM that involve a relationship between two entities, where each entity can be related to multiple instances of the other entity. Let’s go through the provided information step by step: What Are Many-to-Many Relations? In a many-to-many relationship, two entities (A…

Relations in SQL: In the context of databases, a relation refers to the logical association between tables based on common columns. Relations are used to establish connections between tables, enabling you to retrieve and manipulate related data efficiently. There are several types of relationships in SQL: TypeORM: TypeORM is an Object-Relational Mapping (ORM) library for…

Single Table Inheritance TypeORM also supports single table inheritance. Single table inheritance is a pattern when you have multiple classes with their own properties, but in the database they are stored in the same table. This will create a single table called content and all instances of photos, questions and posts will be saved into this table.

Concrete Table Inheritance You can reduce duplication in your code by using entity inheritance patterns. The simplest and the most effective is concrete table inheritance. For example, you have Photo, Question, Post entities: As you can see all those entities have common columns: id, title, description. To reduce duplication and produce a better abstraction we can create a base class called Content for them:…

Embedded entities offer a powerful technique to minimize code duplication within your application by utilizing composition over inheritance. Through the use of embedded columns, you can define a class with its own columns and seamlessly integrate these columns into the database table of the current entity. This approach proves particularly effective when dealing with multiple…