Keep a History of Document Versions

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About this Task

Before you Begin
Steps
Next Steps
Learn More

When your data changes, some applications require that older versions of your data are kept available. In the Document Versioning Pattern, older data versions are retained in a separate collection from the current data.

The Document Versioning Pattern lets you keep current documents and their history in the same database, and avoid having to use multiple systems to manage data history.

About this Task

The Document Versioning Pattern works best if your data meets these criteria:

Documents are updated infrequently.
There are few documents that require version tracking.
Current data and historical data are generally queried separately. In the Document Versioning Pattern, historical data is stored in a separate collection from the current data, so returning both in the same operation can be expensive.

If the preceding criteria do not fit your use case, consider a different solution or change how you implement the Document Versioning Pattern.

Before you Begin

In the following example, an insurance company uses the Document Versioning Pattern to track changes to customer policies. Insert the sample document into the currentPolicies and policyRevisions collections:

db.currentPolicies.insertOne(
   {
      policyId: 1,
      customerName: "Michelle",
      revision: 1,
      itemsInsured: [
         "golf clubs",
         "car"
      ],
      dateSet: new Date()
   }
)

db.policyRevisions.insertOne(
   {
      policyId: 1,
      customerName: "Michelle",
      revision: 1,
      itemsInsured: [
         "golf clubs",
         "car"
      ],
      dateSet: new Date()
   }
)

Steps

With the Document Versioning Pattern, when a policy is updated, the following writes occur:

The policy is updated in the currentPolicies collection. The currentPolicies collection only contains the current data revision of each policyId.
The original policy is written to the policyRevisions collection to keep a record of policy changes.

For example, if the user Michelle wants to add a watch to her policy, the application runs these operations:

Update the policy in the currentPolicies collection

db.currentPolicies.updateOne(
   { policyId: 1 },
   {
      $push: {
         itemsInsured: "watch"
      },
      $inc: {
         revision: 1
      },
      $currentDate: {
         dateSet: true
      }
   }
)

Updated document:

{
   _id: ObjectId("661e873d1a930b8ea1f75c57"),
   policyId: 1,
   customerName: 'Michelle',
   revision: 2,
   itemsInsured: [ 'golf clubs', 'car', 'watch' ],
   dateSet: ISODate("2024-04-16T14:12:24.476Z")
}

Write the updated policy to the policyRevisions collection

db.currentPolicies.aggregate( [
   {
      $match: { policyId: 1 }
   },
   {
      $set: { _id: new ObjectId() }
   },
   {
      $merge: {
         into: { db: "test", coll: "policyRevisions" },
         on: "_id",
         whenNotMatched: "insert"
      }
   }
] )

After you run the previous aggregation, the policyRevisions collection contains both the original and updated policies:

[
   {
      _id: ObjectId("6626c8f02a98aba8ddec31d1"),
      policyId: 1,
      customerName: 'Michelle',
      revision: 1,
      itemsInsured: [ 'golf clubs', 'car' ],
      dateSet: ISODate("2024-04-22T20:30:40.809Z")
   },
   {
      _id: ObjectId("6626c92b2a98aba8ddec31d2"),
      customerName: 'Michelle',
      dateSet: ISODate("2024-04-22T20:31:03.000Z"),
      itemsInsured: [ 'golf clubs', 'car', 'watch' ],
      policyId: 1,
      revision: 2
   }
]

Next Steps

To view a customer's policy history, you can sort the policyRevisions collection by revision. Consider if the customer Michelle makes another change to her policy and no longer wants to insure her golf clubs.

Update the policy in the currentPolicies collection

db.currentPolicies.updateOne(
   { policyId: 1 },
   {
      $pull: {
         itemsInsured: "golf clubs"
      },
      $inc: {
         revision: 1
      },
      $currentDate: {
         dateSet: true
      }
   }
)

Updated document:

{
   _id: ObjectId("661e873d1a930b8ea1f75c57"),
   policyId: 1,
   customerName: 'Michelle',
   revision: 3,
   itemsInsured: [ 'car', 'watch' ],
   dateSet: ISODate("2024-04-16T14:13:38.203Z")
}

Write the updated policy to the policyRevisions collection

db.currentPolicies.aggregate( [
   {
      $match: { policyId: 1 }
   },
   {
      $set: { _id: new ObjectId() }
   },
   {
      $merge: {
         into: { db: "test", coll: "policyRevisions" },
         on: "_id",
         whenNotMatched: "insert"
      }
   }
] )

Return a history of the policy changes

db.policyRevisions.find( { policyId: 1 } ).sort( { revision: 1 } )

Output:

[
   {
      _id: ObjectId("6626c8f02a98aba8ddec31d1"),
      policyId: 1,
      customerName: 'Michelle',
      revision: 1,
      itemsInsured: [ 'golf clubs', 'car' ],
      dateSet: ISODate("2024-04-22T20:30:40.809Z")
   },
   {
      _id: ObjectId("6626c92b2a98aba8ddec31d2"),
      customerName: 'Michelle',
      dateSet: ISODate("2024-04-22T20:31:03.000Z"),
      itemsInsured: [ 'golf clubs', 'car', 'watch' ],
      policyId: 1,
      revision: 2
   },
   {
      _id: ObjectId("6626c9832a98aba8ddec31d3"),
      customerName: 'Michelle',
      dateSet: ISODate("2024-04-22T20:32:43.232Z"),
      itemsInsured: [ 'car', 'watch' ],
      policyId: 1,
      revision: 3
   }
]

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Versioning

Maintain Versions