- 1. API with NestJS #1. Controllers, routing and the module structure
- 2. API with NestJS #2. Setting up a PostgreSQL database with TypeORM
- 3. API with NestJS #3. Authenticating users with bcrypt, Passport, JWT, and cookies
- 4. API with NestJS #4. Error handling and data validation
- 5. API with NestJS #5. Serializing the response with interceptors
- 6. API with NestJS #6. Looking into dependency injection and modules
- 7. API with NestJS #7. Creating relationships with Postgres and TypeORM
- 8. API with NestJS #8. Writing unit tests
- 9. API with NestJS #9. Testing services and controllers with integration tests
- 10. API with NestJS #10. Uploading public files to Amazon S3
- 11. API with NestJS #11. Managing private files with Amazon S3
- 12. API with NestJS #12. Introduction to Elasticsearch
- 13. API with NestJS #13. Implementing refresh tokens using JWT
- 14. API with NestJS #14. Improving performance of our Postgres database with indexes
- 15. API with NestJS #15. Defining transactions with PostgreSQL and TypeORM
- 16. API with NestJS #16. Using the array data type with PostgreSQL and TypeORM
- 17. API with NestJS #17. Offset and keyset pagination with PostgreSQL and TypeORM
- 18. API with NestJS #18. Exploring the idea of microservices
- 19. API with NestJS #19. Using RabbitMQ to communicate with microservices
- 20. API with NestJS #20. Communicating with microservices using the gRPC framework
- 21. API with NestJS #21. An introduction to CQRS
- 22. API with NestJS #22. Storing JSON with PostgreSQL and TypeORM
- 23. API with NestJS #23. Implementing in-memory cache to increase the performance
- 24. API with NestJS #24. Cache with Redis. Running the app in a Node.js cluster
- 25. API with NestJS #25. Sending scheduled emails with cron and Nodemailer
- 26. API with NestJS #26. Real-time chat with WebSockets
- 27. API with NestJS #27. Introduction to GraphQL. Queries, mutations, and authentication
- 28. API with NestJS #28. Dealing in the N + 1 problem in GraphQL
- 29. API with NestJS #29. Real-time updates with GraphQL subscriptions
- 30. API with NestJS #30. Scalar types in GraphQL
- 31. API with NestJS #31. Two-factor authentication
- 32. API with NestJS #32. Introduction to Prisma with PostgreSQL
- 33. API with NestJS #33. Managing PostgreSQL relationships with Prisma
- 34. API with NestJS #34. Handling CPU-intensive tasks with queues
- 35. API with NestJS #35. Using server-side sessions instead of JSON Web Tokens
- 36. API with NestJS #36. Introduction to Stripe with React
- 37. API with NestJS #37. Using Stripe to save credit cards for future use
- 38. API with NestJS #38. Setting up recurring payments via subscriptions with Stripe
- 39. API with NestJS #39. Reacting to Stripe events with webhooks
- 40. API with NestJS #40. Confirming the email address
- 41. API with NestJS #41. Verifying phone numbers and sending SMS messages with Twilio
- 42. API with NestJS #42. Authenticating users with Google
- 43. API with NestJS #43. Introduction to MongoDB
- 44. API with NestJS #44. Implementing relationships with MongoDB
- 45. API with NestJS #45. Virtual properties with MongoDB and Mongoose
- 46. API with NestJS #46. Managing transactions with MongoDB and Mongoose
- 47. API with NestJS #47. Implementing pagination with MongoDB and Mongoose
- 48. API with NestJS #48. Definining indexes with MongoDB and Mongoose
- 49. API with NestJS #49. Updating with PUT and PATCH with MongoDB and Mongoose
- 50. API with NestJS #50. Introduction to logging with the built-in logger and TypeORM
- 51. API with NestJS #51. Health checks with Terminus and Datadog
- 52. API with NestJS #52. Generating documentation with Compodoc and JSDoc
- 53. API with NestJS #53. Implementing soft deletes with PostgreSQL and TypeORM
- 54. API with NestJS #54. Storing files inside a PostgreSQL database
- 55. API with NestJS #55. Uploading files to the server
- 56. API with NestJS #56. Authorization with roles and claims
- 57. API with NestJS #57. Composing classes with the mixin pattern
- 58. API with NestJS #58. Using ETag to implement cache and save bandwidth
- 59. API with NestJS #59. Introduction to a monorepo with Lerna and Yarn workspaces
- 60. API with NestJS #60. The OpenAPI specification and Swagger
- 61. API with NestJS #61. Dealing with circular dependencies
- 62. API with NestJS #62. Introduction to MikroORM with PostgreSQL
- 63. API with NestJS #63. Relationships with PostgreSQL and MikroORM
- 64. API with NestJS #64. Transactions with PostgreSQL and MikroORM
- 65. API with NestJS #65. Implementing soft deletes using MikroORM and filters
- 66. API with NestJS #66. Improving PostgreSQL performance with indexes using MikroORM
- 67. API with NestJS #67. Migrating to TypeORM 0.3
- 68. API with NestJS #68. Interacting with the application through REPL
- 69. API with NestJS #69. Database migrations with TypeORM
- 70. API with NestJS #70. Defining dynamic modules
- 71. API with NestJS #71. Introduction to feature flags
- 72. API with NestJS #72. Working with PostgreSQL using raw SQL queries
- 73. API with NestJS #73. One-to-one relationships with raw SQL queries
- 74. API with NestJS #74. Designing many-to-one relationships using raw SQL queries
- 75. API with NestJS #75. Many-to-many relationships using raw SQL queries
- 76. API with NestJS #76. Working with transactions using raw SQL queries
- 77. API with NestJS #77. Offset and keyset pagination with raw SQL queries
- 78. API with NestJS #78. Generating statistics using aggregate functions in raw SQL
- 79. API with NestJS #79. Implementing searching with pattern matching and raw SQL
- 80. API with NestJS #80. Updating entities with PUT and PATCH using raw SQL queries
- 81. API with NestJS #81. Soft deletes with raw SQL queries
- 82. API with NestJS #82. Introduction to indexes with raw SQL queries
- 83. API with NestJS #83. Text search with tsvector and raw SQL
- 84. API with NestJS #84. Implementing filtering using subqueries with raw SQL
- 85. API with NestJS #85. Defining constraints with raw SQL
- 86. API with NestJS #86. Logging with the built-in logger when using raw SQL
- 87. API with NestJS #87. Writing unit tests in a project with raw SQL
- 88. API with NestJS #88. Testing a project with raw SQL using integration tests
- 89. API with NestJS #89. Replacing Express with Fastify
- 90. API with NestJS #90. Using various types of SQL joins
- 91. API with NestJS #91. Dockerizing a NestJS API with Docker Compose
- 92. API with NestJS #92. Increasing the developer experience with Docker Compose
- 93. API with NestJS #93. Deploying a NestJS app with Amazon ECS and RDS
- 94. API with NestJS #94. Deploying multiple instances on AWS with a load balancer
- 95. API with NestJS #95. CI/CD with Amazon ECS and GitHub Actions
- 96. API with NestJS #96. Running unit tests with CI/CD and GitHub Actions
- 97. API with NestJS #97. Introduction to managing logs with Amazon CloudWatch
- 98. API with NestJS #98. Health checks with Terminus and Amazon ECS
- 99. API with NestJS #99. Scaling the number of application instances with Amazon ECS
- 100. API with NestJS #100. The HTTPS protocol with Route 53 and AWS Certificate Manager
- 101. API with NestJS #101. Managing sensitive data using the AWS Secrets Manager
- 102. API with NestJS #102. Writing unit tests with Prisma
- 103. API with NestJS #103. Integration tests with Prisma
- 104. API with NestJS #104. Writing transactions with Prisma
- 105. API with NestJS #105. Implementing soft deletes with Prisma and middleware
- 106. API with NestJS #106. Improving performance through indexes with Prisma
- 107. API with NestJS #107. Offset and keyset pagination with Prisma
- 108. API with NestJS #108. Date and time with Prisma and PostgreSQL
- 109. API with NestJS #109. Arrays with PostgreSQL and Prisma
- 110. API with NestJS #110. Managing JSON data with PostgreSQL and Prisma
- 111. API with NestJS #111. Constraints with PostgreSQL and Prisma
- 112. API with NestJS #112. Serializing the response with Prisma
- 113. API with NestJS #113. Logging with Prisma
- 114. API with NestJS #114. Modifying data using PUT and PATCH methods with Prisma
- 115. API with NestJS #115. Database migrations with Prisma
- 116. API with NestJS #116. REST API versioning
- 117. API with NestJS #117. CORS – Cross-Origin Resource Sharing
- 118. API with NestJS #118. Uploading and streaming videos
- 119. API with NestJS #119. Type-safe SQL queries with Kysely and PostgreSQL
- 120. API with NestJS #120. One-to-one relationships with the Kysely query builder
- 121. API with NestJS #121. Many-to-one relationships with PostgreSQL and Kysely
- 122. API with NestJS #122. Many-to-many relationships with Kysely and PostgreSQL
- 123. API with NestJS #123. SQL transactions with Kysely
- 124. API with NestJS #124. Handling SQL constraints with Kysely
- 125. API with NestJS #125. Offset and keyset pagination with Kysely
- 126. API with NestJS #126. Improving the database performance with indexes and Kysely
- 127. API with NestJS #127. Arrays with PostgreSQL and Kysely
- 128. API with NestJS #128. Managing JSON data with PostgreSQL and Kysely
- 129. API with NestJS #129. Implementing soft deletes with SQL and Kysely
- 130. API with NestJS #130. Avoiding storing sensitive information in API logs
- 131. API with NestJS #131. Unit tests with PostgreSQL and Kysely
- 132. API with NestJS #132. Handling date and time in PostgreSQL with Kysely
- 133. API with NestJS #133. Introducing database normalization with PostgreSQL and Prisma
- 134. API with NestJS #134. Aggregating statistics with PostgreSQL and Prisma
- 135. API with NestJS #135. Referential actions and foreign keys in PostgreSQL with Prisma
- 136. API with NestJS #136. Raw SQL queries with Prisma and PostgreSQL range types
- 137. API with NestJS #137. Recursive relationships with Prisma and PostgreSQL
- 138. API with NestJS #138. Filtering records with Prisma
- 139. API with NestJS #139. Using UUID as primary keys with Prisma and PostgreSQL
- 140. API with NestJS #140. Using multiple PostgreSQL schemas with Prisma
- 141. API with NestJS #141. Getting distinct records with Prisma and PostgreSQL
- 142. API with NestJS #142. A video chat with WebRTC and React
- 143. API with NestJS #143. Optimizing queries with views using PostgreSQL and Kysely
- 144. API with NestJS #144. Creating CLI applications with the Nest Commander
- 145. API with NestJS #145. Securing applications with Helmet
- 146. API with NestJS #146. Polymorphic associations with PostgreSQL and Prisma
- 147. API with NestJS #147. The data types to store money with PostgreSQL and Prisma
- 148. API with NestJS #148. Understanding the injection scopes
- 149. API with NestJS #149. Introduction to the Drizzle ORM with PostgreSQL
- 150. API with NestJS #150. One-to-one relationships with the Drizzle ORM
- 151. API with NestJS #151. Implementing many-to-one relationships with Drizzle ORM
- 152. API with NestJS #152. SQL constraints with the Drizzle ORM
- 153. API with NestJS #153. SQL transactions with the Drizzle ORM
- 154. API with NestJS #154. Many-to-many relationships with Drizzle ORM and PostgreSQL
- 155. API with NestJS #155. Offset and keyset pagination with the Drizzle ORM
- 156. API with NestJS #156. Arrays with PostgreSQL and the Drizzle ORM
- 157. API with NestJS #157. Handling JSON data with PostgreSQL and the Drizzle ORM
- 158. API with NestJS #158. Soft deletes with the Drizzle ORM
- 159. API with NestJS #159. Date and time with PostgreSQL and the Drizzle ORM
- 160. API with NestJS #160. Using views with the Drizzle ORM and PostgreSQL
- 161. API with NestJS #161. Generated columns with the Drizzle ORM and PostgreSQL
- 162. API with NestJS #162. Identity columns with the Drizzle ORM and PostgreSQL
- 163. API with NestJS #163. Full-text search with the Drizzle ORM and PostgreSQL
- 164. API with NestJS #164. Improving the performance with indexes using Drizzle ORM
- 165. API with NestJS #165. Time intervals with the Drizzle ORM and PostgreSQL
- 166. API with NestJS #166. Logging with the Drizzle ORM
- 167. API with NestJS #167. Unit tests with the Drizzle ORM
- 168. API with NestJS #168. Integration tests with the Drizzle ORM
- 169. API with NestJS #169. Unique IDs with UUIDs using Drizzle ORM and PostgreSQL
- 170. API with NestJS #170. Polymorphic associations with PostgreSQL and Drizzle ORM
- 171. API with NestJS #171. Recursive relationships with Drizzle ORM and PostgreSQL
- 172. API with NestJS #172. Database normalization with Drizzle ORM and PostgreSQL
- 173. API with NestJS #173. Storing money with Drizzle ORM and PostgreSQL
- 174. API with NestJS #174. Multiple PostgreSQL schemas with Drizzle ORM
- 175. API with NestJS #175. PUT and PATCH requests with PostgreSQL and Drizzle ORM
- 176. API with NestJS #176. Database migrations with the Drizzle ORM
- 177. API with NestJS #177. Response serialization with the Drizzle ORM
- 178. API with NestJS #178. Storing files inside of a PostgreSQL database with Drizzle
- 179. API with NestJS #179. Pattern matching search with Drizzle ORM and PostgreSQL
- 180. API with NestJS #180. Organizing Drizzle ORM schema with PostgreSQL
When we work with SQL databases, we usually create tables that relate to each other in some way. Managing those relationships is one of the most fundamental aspects of working with SQL. Across various types of SQL relationships, there is one that sticks out.
Sometimes, one of our tables points back to itself, creating a recursive relationship. This often occurs with hierarchical structures. In this article, we learn more about recursive relationships and how to create them with Prisma.
Recursive relationships are sometimes called self-referencing relationships
Introducing recursive relationships
In the previous parts of this series, we’ve designed a database that uses various types of relationships.
When defining it in the Prisma schema, we use the @relation attribute to define the relationships between our models.
schema.prisma
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model User { id Int @id @default(autoincrement()) email String @unique name String password String articles Article[] address Address? @relation(fields: [addressId], references: [id]) addressId Int? @unique } |
The only exception is when we define an implicit many-to-many relationship. If you want to learn more about defining regular relationships using Prisma, check out API with NestJS #33. Managing PostgreSQL relationships with Prisma
Let’s create a hierarchical structure where a particular article category can have nested categories like this:
- Node.js
- Express
- NestJS
- Integrating with Prisma
- React
- React Hooks
- Testing React
To achieve this, we need to connect the category table to itself. When we want to create a recursive relationship, we also need to use the @relation parameter but we need to name our relationship.
schema.prisma
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model Category { id Int @id @default(autoincrement()) name String articles Article[] parentCategory Category? @relation("CategoriesHierarchy", fields: [parentCategoryId], references: [id]) nestedCategories Category[] @relation("CategoriesHierarchy") parentCategoryId Int? } |
The above schema creates a one-to-many recursive relationship where:
- a particular category can have no more than one parent category,
- multiple categories can share the same parent.
Now, let’s generate a migration.
1 |
npx prisma migrate dev --name add-nested-categories |
migration.sql
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-- AlterTable ALTER TABLE "Category" ADD COLUMN "parentCategoryId" INTEGER; -- AddForeignKey ALTER TABLE "Category" ADD CONSTRAINT "Category_parentCategoryId_fkey" FOREIGN KEY ("parentCategoryId") REFERENCES "Category"("id") ON DELETE SET NULL ON UPDATE CASCADE; |
As we can see, recursive relationships don’t differ too much from regular relationships at first glance regarding the underlying SQL.
Defining the nested categories
One of the ways that we can let the user define the nested categories is by providing them when creating the category.
create-category.dto
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import { IsString, IsNotEmpty, IsInt } from 'class-validator'; import { CanBeUndefined } from '../../utilities/can-be-undefined'; export class CreateCategoryDto { @IsString() @IsNotEmpty() name: string; @IsInt({ each: true }) @CanBeUndefined() nestedCategoryIds?: number[]; } |
If you want to learn more about the @CanBeUndefined decorator, check out API with NestJS #114. Modifying data using PUT and PATCH methods with Prisma
Similarly, we can do that when updating an existing category.
update-category.dto
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import { IsString, IsNotEmpty, IsInt } from 'class-validator'; import { CanBeUndefined } from '../../utilities/can-be-undefined'; export class UpdateCategoryDto { @IsString() @IsNotEmpty() @CanBeUndefined() name?: string; @IsInt({ each: true }) @CanBeUndefined() nestedCategoryIds?: number[]; } |
When making the queries using Prisma, it is important to acknowledge that the user might provide an incorrect category ID in the nestedCategoryIds. When this happens, it violates the foreign key constraint. Fortunately, we can handle that. To do that, we first need to adjust our PrismaError enum.
prisma-enum.ts
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export enum PrismaError { RecordDoesNotExist = 'P2025', UniqueConstraintViolated = 'P2002', ForeignKeyConstraintViolated = 'P2003', ConnectedRecordsNotFound = 'P2018', } |
We can now use the new property of our enum in the categories service.
categories.service.ts
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import { ConflictException, Injectable, NotFoundException, } from '@nestjs/common'; import { PrismaService } from '../database/prisma.service'; import { CreateCategoryDto } from './dto/create-category.dto'; import { Prisma } from '@prisma/client'; import { PrismaError } from '../database/prisma-error.enum'; import { UpdateCategoryDto } from './dto/update-category.dto'; @Injectable() export class CategoriesService { constructor(private readonly prismaService: PrismaService) {} async create(category: CreateCategoryDto) { const nestedCategories = category.nestedCategoryIds?.map((id) => ({ id, })) || []; try { return await this.prismaService.category.create({ data: { name: category.name, nestedCategories: { connect: nestedCategories, }, }, include: { nestedCategories: true, }, }); } catch (error) { if ( error instanceof Prisma.PrismaClientKnownRequestError && error.code === PrismaError.ConnectedRecordsNotFound ) { throw new ConflictException( 'Some of the provided category ids are not valid', ); } throw error; } } async update(id: number, category: UpdateCategoryDto) { try { const nestedCategories = category.nestedCategoryIds?.map((id) => ({ id, })) || []; return await this.prismaService.category.update({ data: { name: category.name, nestedCategories: { connect: nestedCategories, }, }, include: { nestedCategories: true, }, where: { id, }, }); } catch (error) { if (!(error instanceof Prisma.PrismaClientKnownRequestError)) { throw error; } if (error.code === PrismaError.RecordDoesNotExist) { throw new NotFoundException(); } if (error.code === PrismaError.ConnectedRecordsNotFound) { throw new ConflictException( 'Some of the provided category ids are not valid', ); } throw error; } } // ... } |
Querying the nested categories
Connecting a category to its nested categories is relatively easy. However, fetching all of the related nested records might be tricky.
categories.service.ts
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import { Injectable, NotFoundException } from '@nestjs/common'; import { PrismaService } from '../database/prisma.service'; @Injectable() export class CategoriesService { constructor(private readonly prismaService: PrismaService) {} async getById(id: number) { const category = await this.prismaService.category.findUnique({ where: { id, }, include: { articles: true, nestedCategories: true, }, }); if (!category) { throw new NotFoundException(); } return category; } // ... } |
The above approach using nestedCategories: true causes our API to respond with the nested categories.
The problem is that it only returns the first level of nested entities. With Prisma, we must state how deep we want to query explicitly.
categories.service.ts
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import { Injectable, NotFoundException } from '@nestjs/common'; import { PrismaService } from '../database/prisma.service'; @Injectable() export class CategoriesService { constructor(private readonly prismaService: PrismaService) {} async getById(id: number) { const category = await this.prismaService.category.findUnique({ where: { id, }, include: { articles: true, nestedCategories: { include: { nestedCategories: true, }, }, }, }); if (!category) { throw new NotFoundException(); } return category; } // ... } |
PostgreSQL has recursive queries that could solve this problem, but Prisma does not support them yet. As a workaround, we could create a recursive function where we specify the maximum number of levels.
categories.service.ts
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import { Injectable, NotFoundException } from '@nestjs/common'; import { PrismaService } from '../database/prisma.service'; import { Prisma } from '@prisma/client'; @Injectable() export class CategoriesService { constructor(private readonly prismaService: PrismaService) {} getAll() { return this.prismaService.category.findMany(); } private includeNestedCategories( maximumLevel: number, ): boolean | Prisma.Category$nestedCategoriesArgs { if (maximumLevel === 1) { return true; } return { include: { nestedCategories: this.includeNestedCategories(maximumLevel - 1), }, }; } async getById(id: number) { const category = await this.prismaService.category.findUnique({ where: { id, }, include: { articles: true, nestedCategories: this.includeNestedCategories(10), }, }); if (!category) { throw new NotFoundException(); } return category; } // ... } |
Thanks to the includeNestedCategories method, we can fetch deeply nested categories up to a certain level.
Recursive query using raw SQL
If setting the maximum level of the query is not a good enough solution for you, you can use a raw recursive SQL.
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WITH RECURSIVE category_hierarchy AS ( SELECT id, name, 0 as level -- Starting with level 0 for the root category FROM "Category" WHERE id = 1 -- Replace 1 with the id of the category you want to query UNION ALL SELECT category.id, category.name, category_hierarchy.level + 1 -- Incrementing the level for each nested category FROM "Category" category JOIN category_hierarchy category_hierarchy ON category."parentCategoryId" = category_hierarchy."id" ) SELECT * FROM category_hierarchy; |
With this approach, we fetch all deeply nested subcategories of a particular category.
Summary
In this article, we learned how to handle recursive relationships in PostgreSQL using Prisma. To do that, we created an example using categories and subcategories. An interesting part of the example was how to fetch categories along with all its deeply nested subcategories. We had to work around some of the limitations of Prisma to fetch deeply nested entities up to a certain level. If that’s not good enough, we were able to write a raw SQL query that fetches all entities without setting a maximum level. All of this gave us a good idea of how to handle various cases that include recursive relationships.
I did everything carefully as it is written in this article, however, when creating a new category in the database, nothing is created and error:
Foreign key constraint failed on the field:
categories_parentId_fkey (index)