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Transactions in MongoDB allow you to execute multiple operations as a single atomic unit, which either all succeed or all fail.

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How Transactions Work in Orionjs

Orionjs does not provide a specific wrapper for MongoDB transactions. Instead, you can use the native MongoDB transaction API from the underlying MongoDB driver. This approach gives you full control over transaction management while still benefiting from Orionjs’s type safety and validation.

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Using Transactions with Orionjs

To use transactions in Orionjs:
  1. Access the MongoDB client from your collection
  2. Start a session and a transaction
  3. Pass the session to your collection operations
  4. Commit or abort the transaction as needed
import {Repository} from '@orion-js/services'
import {createCollection, typedId} from '@orion-js/mongodb'
import {schemaWithName, InferSchemaType} from '@orion-js/schema'

const AccountSchema = schemaWithName('AccountSchema', {
  _id: {type: typedId('account')},
  balance: {type: Number},
  owner: {type: String}
})

const TransactionSchema = schemaWithName('TransactionSchema', {
  _id: {type: typedId('trx')},
  fromId: {type: String},
  toId: {type: String},
  amount: {type: Number},
  date: {type: Date}
})

type AccountType = InferSchemaType<typeof AccountSchema>
type TransactionType = InferSchemaType<typeof TransactionSchema>

@Repository()
export class AccountRepository {
  accounts = createCollection({
    name: 'accounts',
    schema: AccountSchema
  })

  transactions = createCollection({
    name: 'transactions',
    schema: TransactionSchema
  })

  async transferFunds(fromId: string, toId: string, amount: number) {
    // Get the MongoDB client from the collection
    const client = this.accounts.client.client;
    
    // Start a session
    const session = client.startSession();
    
    try {
      // Start a transaction
      session.startTransaction();
      
      // Deduct from source account
      const sourceUpdateResult = await this.accounts.updateOne(
        {_id: fromId, balance: {$gte: amount}},
        {$inc: {balance: -amount}},
        {mongoOptions: {session}} // Pass the session to the operation
      );
      
      if (sourceUpdateResult.modifiedCount === 0) {
        // Abort the transaction if no document was updated
        await session.abortTransaction();
        throw new Error('Insufficient funds');
      }
      
      // Add to destination account
      await this.accounts.updateOne(
        {_id: toId},
        {$inc: {balance: amount}},
        {mongoOptions: {session}} // Pass the session to the operation
      );
      
      // Record the transaction
      await this.transactions.insertOne(
        {
          fromId,
          toId,
          amount,
          date: new Date()
        }, 
        {mongoOptions: {session}} // Pass the session to the operation
      );
      
      // Commit the transaction
      await session.commitTransaction();
      return true;
    } catch (error) {
      // Abort the transaction on error
      await session.abortTransaction();
      throw error;
    } finally {
      // End the session
      await session.endSession();
    }
  }
  
  // Alternative implementation using withTransaction
  async transferFundsWithTransaction(fromId: string, toId: string, amount: number) {
    const client = this.accounts.client.client;
    const session = client.startSession();
    
    try {
      // Use the withTransaction helper from the MongoDB driver
      return await session.withTransaction(async () => {
        // Deduct from source account
        const sourceUpdateResult = await this.accounts.updateOne(
          {_id: fromId, balance: {$gte: amount}},
          {$inc: {balance: -amount}},
          {mongoOptions: {session}}
        );
        
        if (sourceUpdateResult.modifiedCount === 0) {
          throw new Error('Insufficient funds');
        }
        
        // Add to destination account
        await this.accounts.updateOne(
          {_id: toId},
          {$inc: {balance: amount}},
          {mongoOptions: {session}}
        );
        
        // Record the transaction
        await this.transactions.insertOne(
          {
            fromId,
            toId,
            amount,
            date: new Date()
          }, 
          {mongoOptions: {session}}
        );
        
        return true;
      });
    } finally {
      await session.endSession();
    }
  }
}

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Important Notes About Sessions

When using sessions with Orionjs collection methods:
  1. Pass the session in the mongoOptions object: 
    await collection.updateOne(
  filter,
  update,
  {mongoOptions: {session}}
);
  2. All DataLoader methods bypass the session, so avoid using them within transactions.
  3. You must explicitly commit or abort the transaction, and end the session.

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Prerequisites

  • MongoDB 4.0+ for replica set deployments
  • MongoDB 4.2+ for sharded cluster deployments
  • Your MongoDB connection must be to a replica set or sharded cluster (not a standalone server)

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Best Practices

  1. Keep Transactions Short: Long-running transactions can lead to performance issues
  2. Handle Errors: Always handle errors to ensure transactions are properly aborted when needed
  3. Consider Read Concerns: For critical operations, use appropriate read and write concerns
  4. Check Modification Results: Always check the results of update operations to verify they modified the expected documents
  5. Avoid Unnecessary Work: Only include operations that need atomicity in your transactions
  6. Watch for Transaction Errors: Be prepared to handle transaction-specific errors like session timeout
Transactions provide a powerful way to ensure data consistency across multiple MongoDB operations while using Orionjs.
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