Top 8 Tips for Using Prisma with MongoDB

Today, I'm sharing the top eight tips for using Prisma ORM with MongoDB. If you're building applications with MongoDB and want to use Prisma as your ORM, there are some important considerations you need to know. MongoDB's document-based approach works differently from relational databases, and Prisma ORM has specific ways of handling these differences.

I've spent years working with both MongoDB and Prisma ORM, and I've compiled the most critical tips that will save you hours of debugging and help you build more efficient applications. These aren't just basic setup instructions—these are the practical insights that make the difference between a struggling application and one that performs smoothly in production.

If you'd rather watch, here's a video version:

Tip #1: Configure MongoDB with a replica set

MongoDB with Prisma ORM requires a replica set configuration. This isn't optional—it's mandatory. Prisma uses transactions internally to avoid partial writes on nested queries, and MongoDB only allows transactions on replica sets.

If you try to use Prisma ORM with a standalone MongoDB instance, you'll get the error, "Transactions are not supported by this deployment." This happens even for simple operations because Prisma wraps operations in transactions behind the scenes.

The easiest solution is to use MongoDB Atlas, which provides replica sets by default, even on the free tier. For local development, you can convert a standalone MongoDB instance to a replica set by following MongoDB's documentation.

Tip #2: Working with ObjectId fields

In MongoDB, the primary key is typically an ObjectId stored in the _id field. When working with Prisma ORM, you need to properly map this in your schema.

Any field that maps to an ObjectId in MongoDB:

• Must be defined as either String or Bytes type in your Prisma schema.
• Must include the @db.ObjectId attribute.
• Should use @default(auto()) for auto-generating IDs.

Here's how to define a model with an ObjectId primary key:

model User {
  id    String @id @default(auto()) @map("_id") @db.ObjectId
  email String
  name  String?
}

When you need to generate an ObjectId for testing or to manually set an ID, use the bson package:

import { ObjectId } from 'bson'
const id = new ObjectId()

Tip #3: Understand the difference between null and missing fields

MongoDB distinguishes between fields explicitly set to null and fields that don't exist at all. There's this thing called polymorphism in MongoDB. It's the ability to have multiple types of data in the same collection. This distinction is important when filtering data.

When you create a record without explicitly setting an optional field, MongoDB doesn't store that field at all. But, Prisma ORM will return null for that field in your query results, making it appear the same as a field explicitly set to null.

When filtering for null values, you'll only match records where the field is explicitly set to null, not records where the field is missing. To include missing fields in your filter, use the isSet operator:

// Find records where name is either null or missing
const users = await prisma.user.findMany({
  where: {
    OR: [
      { name: null },
      { name: { isSet: false } }
    ]
  }
})

Tip #4: Handle relations properly

MongoDB handles relationships through document references and embedded documents, which differs from the foreign key approach in relational databases. When introspecting a MongoDB database, Prisma ORM may need help understanding these relationship patterns.

After introspection, you'll need to manually add relation fields to your models. For example, if you have a Post model with a userId field, you'll need to add the relation to the User model:

model Post {
  id     String @id @default(auto()) @map("_id") @db.ObjectId
  title  String
  userId String @db.ObjectId
  user   User   @relation(fields: [userId], references: [id])
}

model User {
  id    String @id @default(auto()) @map("_id") @db.ObjectId
  email String
  posts Post[]
}

Remember that relation fields in MongoDB should always use the @db.ObjectId attribute when they reference another document's ID.

Tip #5: Model embedded documents with type

MongoDB's document model allows you to embed structured data directly within a document. This is one of MongoDB's core advantages—the ability to store related data in a single document, reducing the need for joins. Prisma ORM supports this pattern through the type keyword.

Unlike models, types in Prisma don't create separate collections in MongoDB. Instead, they represent embedded document structures that exist inside a model.

Here's how to define and use embedded types:

type Address {
  street  String
  city    String
  state   String
  zipCode String
}

model Customer {
  id        String   @id @default(auto()) @map("_id") @db.ObjectId
  name      String
  email     String   @unique
  address   Address? // Embedded document
  addresses Address[] // Array of embedded documents
}

When working with these embedded types in your code:

// Creating a record with embedded document
const customer = await prisma.customer.create({
  data: {
    name: 'Jane Smith',
    email: '[e-mail]',
    address: {
      street: '123 Main St',
      city: 'Anytown',
      state: 'CA',
      zipCode: '12345'
    }
  }
})

// Querying with embedded fields
const californiaCustomers = await prisma.customer.findMany({
  where: {
    address: {
      state: 'CA'
    }
  }
})

Embedded documents work well for data that:

• Is always accessed together with the parent document.
• Has a clear ownership relationship (belongs to exactly one parent).
• Doesn't need to be queried independently.

Tip #6: Simplified schema management with MongoDB

MongoDB's flexible schema design eliminates the need for complex migrations. You can modify your data model without downtime or migration scripts—a key advantage over traditional databases.

With Prisma ORM and MongoDB, use prisma db push to sync your schema changes. This command will:

• Create collections if they don't exist.
• Set up indexes for @unique fields.
• Update your Prisma Client automatically.

Tip #7: Key MongoDB and Prisma design considerations

Here are some important key points to consider when using Prisma ORM with MongoDB:

1. MongoDB uses a single _id field for primary keys, rather than composite IDs with @@id.
2. For ID generation, use auto() with ObjectId instead of autoincrement().
3. Cyclic references with referential actions work best with NoAction to maintain data consistency.
4. Some MongoDB-specific types, like Decimal128, have partial support in the current version of Prisma ORM.

These points highlight the fundamental differences between how document databases and relational databases work. When you know these technical distinctions, you can create applications that work better with MongoDB's specific structure.

Tip #8: Optimize for large collections

MongoDB performance can degrade with large collections if you're not careful when using Prisma ORM. Consider these tips to help you optimize your queries:

1. Be strategic with indexes—add @index to fields you frequently query on.
2. Use projection to limit returned fields—use select to specify only the fields you need.
3. Paginate results—use skip and take to limit the number of documents processed.
4. Consider using MongoDB's aggregation pipeline for complex operations via Prisma's $runCommandRaw.

For example, to optimize a query on a large collection:

const users = await prisma.user.findMany({
  where: { role: "ADMIN" },
  select: { id: true, email: true }, // Only select needed fields
  take: 100, // Limit to 100 results
  skip: page * 100, // Pagination
})

Conclusion

These eight tips will help you effectively use Prisma ORM with MongoDB while avoiding common pitfalls. Remember that MongoDB's document model is fundamentally different from relational databases, and understanding these differences is key to building performant applications.

Check out my complete walkthrough of building a full-stack app with Next.js + Prisma ORM + MongoDB to see it in action.

To recap, always use a replica set configuration, handle ObjectIds correctly, understand the difference between null and missing fields, manage relations properly, use db push instead of migrations, adapt to MongoDB's document model features, and optimize for large collections.

Drop a comment if you have questions about using Prisma ORM with MongoDB or if you'd like to see more in-depth coverage of any of these topics.

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