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Solving the NestJS Sequelize One-to-One Foreign Key Constraint Error in PostgreSQL

Discover how to resolve the common foreign key constraint error in NestJS using Sequelize with PostgreSQL. Learn about the @ HasOne and @ BelongsTo decorators for proper table relationships. --- This video is based on the question https://stackoverflow.com/q/71556739/ asked by the user 'kedO52' ( https://stackoverflow.com/u/17695704/ ) and on the answer https://stackoverflow.com/a/71558588/ provided by the user 'kedO52' ( https://stackoverflow.com/u/17695704/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Nest Postgresql Sequelize one-to-one Error with ForeignKey Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- How to Fix NestJS PostgreSQL Sequelize One-to-One Foreign Key Constraint Error When working with relational databases, setting up the correct associations between your tables is crucial. In the context of a NestJS application using Sequelize with PostgreSQL, developers may encounter foreign key constraint errors, especially in one-to-one relationships. This guide explores a scenario where such an error appears and provides a straightforward solution. The Problem: Foreign Key Constraint Error In our example, we have two tables, siCheckingInfo (the primary table) and checkingResults (the related table). The issue arises when attempting to insert data into the checkingResults table. Here’s the specific error message encountered: [[See Video to Reveal this Text or Code Snippet]] This constraint error indicates that an attempt is being made to insert a value in checkingResults that does not have a corresponding entry in the siCheckingInfo table as per the foreign key relation set. Key Elements of the Table Structure siCheckingInfo Table (Primary) [[See Video to Reveal this Text or Code Snippet]] checkingResults Table (Related) [[See Video to Reveal this Text or Code Snippet]] Why the Error Occurs The error typically occurs when the foreign key relationships configured do not align correctly with the actual data entries in the database. In this specific situation, we encountered the statement @ ForeignKey and @ BelongsTo decorators being incorrectly placed, which led to the failed foreign key constraint when inserting values. The Solution: Adjusting the Decorators To resolve this issue, it is essential to adjust the placement of the decorators associated with the relationship between siCheckingInfo and checkingResults. Here are the steps to do that: Change the Order of Decorators: Move the @ HasOne decorator to mark the relationship from the child to the parent table (checkingResults to siCheckingInfo). Move the @ BelongsTo decorator to indicate the correct relationship from the parent (siCheckingInfo) to the child (checkingResults). Here’s how the corrected code should look: Updated Code for siCheckingInfo Table [[See Video to Reveal this Text or Code Snippet]] Updated Code for CheckingResults Table [[See Video to Reveal this Text or Code Snippet]] Conclusion By placing the correct decorators for the one-to-one relationship between siCheckingInfo and checkingResults, we eliminate the foreign key constraint error. This adjustment ensures that Sequelize understands how to associate the two models seamlessly. If you encounter this or similar issues in your own projects, remember to inspect the corresponding relationships and ensure that your foreign key declarations are properly aligned. For any further questions or discussions on Sequelize relationships, feel free to leave comments below!