Enforcing Dependency Constraints in Nx Monorepo Projects

4 minute read

Are you using NRWL/NX monorepo in your company? and you are worried how to configure dependencies so that you can better control your projects? I use nx dependency constraints to restrict which project can depend on whom just like you do in .net or java or any typed language. Read this article to understand how you can configure dependency constraint and visualize your monorepo workspace dependency graph.

Why do you need dependency enforcement?

In Nx Monorepo workspace we can have applications (apps) and libraries (libs). Apps will have projects that are hosted on the server. Libs should have the projects which are supporting Apps. Inside the Libs folder you can have your service projects. Within the Libs we end up creating lots of projects and it is very confusing when every project can depend on every other project.

However, If you want to partition service code into well-defined cohesive blocks. Especially if you are following Service Oriented Architecture Advanced Distributed Systems Design by Udi Dahan. Then you might be aware that one service code should not depend on another service code. Therefore, you want to impose constraints on how projects can depend on each other in JavaScript Projects. Then it is very difficult if you don’t use any framework. I would highly recommend using Nx Monorepo tag and scope.

Read this article till the end to learn more!

Understanding Monorepo workspace projects

In my monorepo you can notice I have 3 folders:

  1. Branding folder that has 3 projects like logger, layout, angular material
  2. Sales folder that has 2 projects like product-editor and products
  3. Customers folder that has 2 projects like user-editor and users

Defining which project can depend on whom

Below are the dependency rules I want to enforce in my monorepo.

  • Sales projects:
    • Can depend on Branding projects
    • Can not depend on Customers projects
  • Customers projects:
    • Can depend on Branding projects
    • Can not depend on Sales projects
  • Branding projects:
    • Can not depend on Sales projects
    • Can not depend on Customers projects

Good news is you can do dependency enforcement free in Nx Monorepo using configuration. So follow the steps below.

Step 1: Adding Project’s Tags in Nx.json

Go to nx.json and add projects tags.

"projects": {
    "sales-product-editor": {
      "tags": [
        "scope:sales"
      ]
    },
    "sales-products": {
      "tags": [
        "scope:sales"
      ]
    },
    "customers-user-editor": {
      "tags": [
        "scope:customers"
      ]
    },
    "customers-users": {
      "tags": [
        "scope:customers"
      ]
    },
    "shared-ng-material": {
      "tags": [
        "scope:branding"
      ]
    },
    "shared-layout": {
      "tags": [
        "scope:branding"
      ]
    },
    "shared-logger": {
      "tags": [
        "scope:branding"
      ]
    },
     "onlinestore-client-e2e": {
      "tags": [],
      "implicitDependencies": [
        "onlinestore-client"
      ]
    },
    "onlinestore-admin-e2e": {
      "tags": [],
      "implicitDependencies": [
        "onlinestore-admin"
      ]
    },
       "onlinestore-client": {
      "tags": [
        "type:app",
        "scope:client"
      ]
    },
    "onlinestore-admin": {
      "tags": [
        "type:app",
        "scope:admin"
      ]
    },
    "onlinestore-client-e2e": {
      "tags": [],
      "implicitDependencies": [
        "onlinestore-client"
      ]
    },
    "onlinestore-admin-e2e": {
      "tags": [],
      "implicitDependencies": [
        "onlinestore-admin"
      ]
    }
  }

Step 2: Adding Dependency Enforcement in tslint.json file

Add below nx-enforce-module-boundaries array in tslint.json file.

 "nx-enforce-module-boundaries": [
      true,
      {
        "enforceBuildableLibDependency": true,
        "allow": [],
        "depConstraints": [
          {
            "sourceTag": "scope:sales",
            "onlyDependOnLibsWithTags": [
              "scope:sales",
              "scope:branding"
            ]
          },
          {
            "sourceTag": "scope:customers",
            "onlyDependOnLibsWithTags": [
              "scope:customers",
              "scope:branding"
            ]
          },
          {
            "sourceTag": "scope:branding",
            "onlyDependOnLibsWithTags": [
              "scope:branding"
            ]
          }
        ]
      }
    ],

Testing the boundary constraint

Now if you go to sales-products.module.ts and perform below imports.

Remember the Rule for Sales Service: 👍

  • Sales projects
    • can depend on Branding projects
    • can depend on other Sales projects
    • can not depend on Customers projects

Testing Sales projects dependency rules live

  1. Try to import SharedLoggerModule from branding scope and run npm run affected:lint you will not see any error.
// sales project
import { SharedLoggerModule } from "@myorg/shared/logger";
  1. Try to import CustomersUserEditorModule from Customers scope and run npm run affected:lint you will see any error.
// Sales project can not depend on Customers project
import { CustomersUserEditorModule } from "@myorg/customers-user-editor";

You will see below error:

> ng run sales-products:lint
Linting "sales-products"...
C:/Projects/GitHub/nx-repo/myorg/myorg/libs/sales/products/src/lib/sales-products.module.ts:9:1
ERROR: 9:1  nx-enforce-module-boundaries  A project tagged
with "scope:sales" can only depend on libs tagged with "scope:sales", "scope:branding"

  1. Try to import SalesProductEditorModule Project from sales service only and and run npm run affected:lint you will not see any error.
// Sales project can depend on other sales project
import { SalesProductEditorModule } from "@myorg/sales-product-editor";

Conclusion

So I loved the way Nx Monorepo framework gives the boundary constraints out of the box.

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