Скачать или смотреть Fixing leftJoinAndSelect in NestJS for Complete PostgreSQL Data Retrieval

Learn how to resolve issues with NestJS's `leftJoinAndSelect` when working with PostgreSQL to ensure all necessary data is retrieved correctly.
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This video is based on the question https://stackoverflow.com/q/72416288/ asked by the user 'Mohammad Khair' ( https://stackoverflow.com/u/8139353/ ) and on the answer https://stackoverflow.com/a/72443716/ provided by the user 'Mohammad Khair' ( https://stackoverflow.com/u/8139353/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing leftJoinAndSelect in NestJS for Complete PostgreSQL Data Retrieval

When working with databases in a NestJS application, especially when using TypeORM with PostgreSQL, you may encounter issues retrieving related data. One of the common scenarios involves using leftJoinAndSelect to fetch related entities from different tables. If your query returns incomplete data, don't panic! In this guide, we will walk through a specific problem involving three tables and provide a detailed solution so that you can successfully retrieve all necessary data.

The Problem

In this scenario, the user has three related tables: product, branch, and product_branches. The structure for these tables is as follows:

product: Contains id and name

branch: Contains id, name, lat, and lng

product_branches: Contains productId and branchId

The initial query using leftJoinAndSelect didn't return the expected results. Instead of retrieving the complete object with branches included, the returned data only consisted of the product details. Here’s what it looked like:

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

What was desired was a result that also included the related branches, like so:

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

The Solution

The solution to this issue lies in examining two key aspects of your code: the use of the @ Exclude decorator and the method of retrieving data.

1. Adjusting the @ Exclude Decorator

In the ProductBranches entity, the property for the branch had the @ Exclude({ toPlainOnly: true }) decorator applied, which prevented it from being serialized and returned in the final output. To fix this, you will need to remove or adjust this decorator:

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

2. Updating the Data Retrieval Method

Instead of using createQueryBuilder, it may be more effective to use the find method provided by TypeORM. The updated query would look like this:

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

3. Returning Branches within ProductBranches

It’s important to note that with this adjustment, the branch data will appear nested within the productBranches array rather than as a separate JSON object. Here's how this looks:

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

Conclusion

By appropriately adjusting the use of decorators and methods for data retrieval, you can ensure that your queries return the complete set of related data as expected. This fix not only clarifies how to structure your queries properly in NestJS but also enhances your understanding of both TypeORM relationships and decorators.

Thanks to community members like Mohammad Ali for the assistance, and happy coding!