TypeORM - Converting SQL LEFT JOIN One-to-One Relation into TypeORM Query Builder

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Mastering TypeORM: Converting SQL LEFT JOIN One-to-One Relations into TypeORM Query Builder

In modern web applications, interacting with databases efficiently is crucial. TypeORM is a powerful ORM for TypeScript and JavaScript that enables developers to work with databases seamlessly. However, sometimes transitioning from traditional SQL statements into TypeORM's Query Builder can be challenging. A common scenario is converting a SQL LEFT JOIN query to its TypeORM equivalent, especially when working with one-to-one relationships. This guide aims to break down the problem and provide a clear, structured solution.

The Problem: Joining Entities with TypeORM

You have defined two entities in your PostgreSQL database using TypeORM, Issuer and UserData. The Issuer entity has a one-to-one relationship with UserData. You want to retrieve data from both entities using a LEFT JOIN. Your SQL query is neatly structured:

[[See Video to Reveal this Text or Code Snippet]]

However, when attempting to convert this SQL code to a TypeORM query builder style, you encountered an error indicating that the relation with the property path public_address was not found. This is a common hurdle when transitioning between SQL and ORM-based queries.

Solution Approach: Using leftJoinAndSelect

The underlying issue arises because the direct relation needed for the leftJoin method does not exist in the UserData entity based on how you set up the relationships. Instead, you need to use the leftJoinAndSelect method with an additional condition. Here’s how to do it correctly:

Step-by-Step Conversion

Retrieve the Repository: First, ensure you have the repository for your UserData entity available.

Use createQueryBuilder: Begin building your query with createQueryBuilder(), specifying the alias for your entity.

Implement leftJoinAndSelect method: This method allows you to join other entities with a condition. Specify both the target entity and the condition that reflects your SQL statement.

Specify the Condition: Ensure you properly define how the two tables relate to one another.

The Correct Code

Here’s the corrected TypeORM code that performs the desired operation:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

createQueryBuilder('user'): This initializes the query with user as an alias for the UserData entity.

.getRawOne(): This method fetches the result, returning a single record.

Conclusion

Converting SQL LEFT JOIN queries into TypeORM query builder formats is not just about finding equivalents; it also requires a solid understanding of how relationships are set up in the entities. By following the structured method outlined above, you can successfully retrieve data while taking advantage of TypeORM’s powerful features.

Keep this guide handy for any future queries you may need to convert, and happy coding!