fix: new MongoDB projects install with npm instead of failing with ERESOLVE

[wmadden-electric]

Fixes #114

At a glance

Command: npm create prisma@latest -- --provider mongodb --no-deploy

	Before (create-prisma 0.13.3)	After
Result	npm install fails with npm error code ERESOLVE. The command exits 1.	npm install succeeds. The command exits 0.
overrides in the generated package.json	{ "effect": "4.0.0-rc.115" }	{ "effect": "4.0.0-rc.115", "alchemy": { "mongodb": "^7.1.0" } }

What this pull request does

When create-prisma scaffolds a MongoDB project for npm, it now writes an npm override that tells npm which version of the mongodb package to use for the alchemy package. With that override, the install succeeds. For pnpm, it writes a rule that removes the warning about the same conflict.

Background

Every scaffolded project depends on @prisma/composer, and @prisma/composer depends on alchemy. A MongoDB project also depends on @prisma/orm-mongo and on mongodb, the MongoDB driver.

Two of these packages ask for different major versions of the driver:

• @prisma/orm-mongo requires mongodb@^7.0.0.
• alchemy declares an optional peer dependency on mongodb@^6.10.0.

npm treats this as a conflict that it cannot resolve, and stops the install. This is the relevant part of its output:

npm error code ERESOLVE
npm error ERESOLVE could not resolve
npm error
npm error While resolving: alchemy@2.0.0-beta.78
npm error Found: mongodb@7.6.0
npm error node_modules/mongodb
npm error   mongodb@"^7.1.0" from the root project
npm error   peer mongodb@"^7.0.0" from @prisma/orm-mongo@8.0.0-rc.12
npm error
npm error Could not resolve dependency:
npm error peerOptional mongodb@"^6.10.0" from alchemy@2.0.0-beta.78

The other package managers do not stop. pnpm and Yarn print a warning. Bun prints nothing.

The conflict has no effect when the project runs. alchemy uses the driver only in modules that the scaffolded project never loads.

Updating the packages does not remove the conflict. alchemy@2.0.0-beta.79 is the latest release and still declares mongodb@^6.10.0. @prisma/composer@0.23.0 is the latest release and requires alchemy@2.0.0-beta.78 exactly.

The change

npm. In src/tasks/install.ts, writePrismaDependenciesEffect now adds "alchemy": { "mongodb": "^7.1.0" } to overrides in the root package.json. It does this only when the provider is MongoDB and the package manager is npm. The version is the mongodb entry in dependencyVersionMap, which is the same version that the project installs. The existing effect override is kept.

pnpm. templates/create/_package-manager/pnpm-workspace.yaml.hbs now adds this for MongoDB projects:

peerDependencyRules:
  allowedVersions:
    "alchemy>mongodb": "7"

Tests. The unit test in tests/install.test.ts checks the generated overrides and pnpm-workspace.yaml for each provider and package manager. A new end-to-end test in tests/e2e/create-prisma.e2e.test.ts scaffolds a MongoDB project with npm and installs it. It checks that the installed driver is version 7 and that alchemy has no second copy of the driver. It then emits the contract, builds, type checks, and starts the built server against an in-memory MongoDB from mongodb-memory-server. It expects status 200 and the users Alice, Bob, and Carol.

What was checked

Continuous integration on this pull request passes. It runs bun run check, bun run typecheck, bun run check:pins, bun run test:unit, and bun run build, and a scaffold test on Windows. It does not run the end-to-end tests.

These were run locally with the built command line tool and --no-deploy:

Template	Provider	Package manager	Result
minimal	MongoDB	npm	Exit 0. npm ls mongodb shows one copy, mongodb@7.6.0.
minimal	MongoDB	pnpm	Exit 0. pnpm peers check prints "No peer dependency issues found".
minimal	MongoDB	Yarn	Exit 0.
minimal	MongoDB	Bun	Exit 0.
turborepo	MongoDB	npm	Exit 0.
minimal	PostgreSQL	npm	Exit 0.

Also run locally: bun run test:unit (86 pass) and bun run test:e2e (12 pass). Without the change, the new end-to-end test fails with ERESOLVE.

What this does not do

• PostgreSQL projects are unchanged.
• Yarn still prints warning YN0060 for this peer dependency. The install succeeds.
• Nothing was deployed during testing.
• The override can be removed when alchemy accepts mongodb 7 and @prisma/composer requires that alchemy release.

Alternatives considered

• Install with --legacy-peer-deps or --force. These turn off peer dependency checks for every package, so npm would no longer report other conflicts. The override affects only the mongodb peer dependency of alchemy.
• Write the override as "$mongodb". This npm syntax means "use the version from the root package.json". In the turborepo template the root package.json does not list mongodb. Only packages/database lists it, so the reference would not resolve.

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Summary by CodeRabbit

• Bug Fixes
  • Improved setup for Prisma projects using MongoDB, helping ensure compatible MongoDB dependency versions are selected with npm and pnpm.
  • Added coverage for building, type-checking, and running a MongoDB-backed project with an in-memory replica set.

Walkthrough

MongoDB projects using npm now receive an alchemy.mongodb override set to the mapped MongoDB dependency version. MongoDB projects using pnpm now allow version 7 for the alchemy>mongodb peer dependency. Tests check package-manager overrides and exercise a generated MongoDB project through build, type-check, and runtime verification against an in-memory replica set.

Priority: ➖ Normal

Severity of issue fixed: Medium

Merge Risk: 🟡 Moderate · up to c6f11

MongoDB setup can silently discard an existing npm dependency override in a non-empty project. Preserve that override before merging.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to c6f11

For MongoDB projects using npm, setup can replace an existing Alchemy dependency override. This could remove a version pin chosen by the project, although the effect is limited to projects with a conflicting override.

Retained concerns

• Medium · security · inferred: MongoDB npm setup replaces an existing overrides.alchemy value rather than preserving its package pin or other nested overrides. In a reused project, this can remove a project-owned dependency constraint before installation.

Security review details

Security Blast Radius

• inferred — Exposure is confined to manifests processed as MongoDB/npm projects and their subsequent dependency installs. The evidence does not establish a remotely reachable endpoint or a cross-tenant privilege change.

Security Findings and Attack Paths

• inferred — If a reused project has an Alchemy override serving as a dependency security pin, the new assignment removes that pin before npm resolves packages. Whether any affected project has such a pin, or an attacker can exploit its removal, is unverified.

Trust Boundaries and Controls

• observed — Setup passes its selected provider and package manager to dependency writing, which gates the npm override on both values. The helper preserves unrelated top-level overrides but does not preserve ownership within overrides.alchemy.

Resilience and Maintainability Implications

• inferred — Sequential repetition rewrites the same MongoDB override, but the read-and-write sequence has no visible conflict check. The scoped evidence does not establish how concurrent writers or an interrupted file write recover.

Hardening Proposals

• proposed — Define how setup handles a pre-existing Alchemy override: preserve compatible project-owned constraints or fail with an explicit conflict rather than silently replacing the namespace.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 3 files. (1 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue #114 requires a fix for the npm ERESOLVE conflict between alchemy and @prisma/orm-mongo. The PR adds an npm alchemy.mongodb override that uses the MongoDB dependency version. It adds the…
Out of Scope Changes check	✅ Passed	The changes stay within Issue #114. The source change updates package-manager dependency resolution. The pnpm configuration supports the same MongoDB peer conflict. The install matrix and E2E changes …
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing npm installation failures for new MongoDB projects caused by ERESOLVE.
Description check	✅ Passed	The description directly explains the npm and pnpm changes, the dependency conflict, test coverage, validation results, and scope. It is fully related to the changeset.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 3 files. (1 skipped: 1 unsupported.)

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Inline comments:
Review comments at @src/tasks/install.ts:
- Line 169: Update the `alchemy` entry in the overrides assignment to merge
existing nested entries when adding `mongodb`; if the existing
`overrides.alchemy` value is a string, preserve it using npm’s `"."` package
override form.

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📥 Commits

Reviewing files that changed from the base of the PR and between 3c9947f and c6f11de.

📒 Files selected for processing (4)

• src/tasks/install.ts
• templates/create/_package-manager/pnpm-workspace.yaml.hbs
• tests/e2e/create-prisma.e2e.test.ts
• tests/install.test.ts

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PR preview published

• Version: 0.13.3-pr.116.382.1
• Tag: pr116
• Run with Bun: bunx create-prisma@pr116
• Run with npm: npx create-prisma@pr116
• Run with Yarn: yarn dlx create-prisma@pr116
• Run with pnpm: pnpm dlx create-prisma@pr116
• Run with Deno: deno run -A --minimum-dependency-age=0 npm:create-prisma@pr116
• Workflow run: https://github.com/prisma/create-prisma/actions/runs/36395810729