Migration to add age bucketing field to cases schema #2670

data-serving/scripts/setup-db/migrations/20220420100113-add-age-buckets.js

@@ -0,0 +1,77 @@
+/*
+ * We need to ensure that ages are bucketed within five-year brackets, except for infants (below 1 year)
+ * to improve the protection against deanonymisation in the case database. In this migration I create an
+ * ageBuckets collection which represents an enumeration of the age ranges 0, 1-5, 6-10, 11-15, ..., 116-120.
+ * 
+ * I also allow the cases collection documents to have an array of unique objectIDs in the 'demographics.ageBuckets'
+ * property. That means that each case can link to zero or more elements in the enumeration. Here are some examples of
+ * how that will work:
+ * 
+ * case has no age specified: ageBuckets = []
+ * case has exact age 18: ageBuckets = [(16-20)._id]
+ * case has range 18-24: ageBuckets = [(16-20)._id, (21-25)._id]
+ */
+
+const ageBucketSchema = {
+  bsonType: 'array',
+  uniqueItems: true,
+  items: {
+    bsonType: "objectId",
+  }
+};
+
+module.exports = {
+  async up(db, client) {
+    await db.createCollection("ageBuckets", {
+      validator: {
+        $jsonSchema: {
+          "bsonType": "object",
+          "additionalProperties": false,
+          "required": ["start", "end"],
+          "properties": {
+            "_id": {
+              "bsonType": "objectId",
+            },
+            "start": {
+              "bsonType": "number",
+              "minimum": 0,
+              "maximum": 116
+            },
+            "end": {
+              "bsonType": "number",
+              "minimum": 0,
+              "maximum": 120
+            }
+          }
+        }
+      }
+    });
+
+    const ageBuckets = db.collection('ageBuckets');
+    await ageBuckets.insertOne({
+      start: 0,
+      end: 0,
+    });
+    for(let start = 1; start <= 116; start += 5) {
+      const end = start + 4;
+      await ageBuckets.insertOne({
+        start,
+        end,
+      });
+    }
+
+    let res = await db.command({listCollections: undefined, filter: {name: 'cases'}});
+    let schema = res.cursor.firstBatch[0].options.validator.$jsonSchema;
+    schema.properties.demographics.properties.ageBuckets = ageBucketSchema;
+    await db.command({ collMod: 'cases', validator:{ $jsonSchema: schema } } );
+  },
+
+  async down(db, client) {
+    let res = await db.command({listCollections: undefined, filter: {name: 'cases'}});
+    let schema = res.cursor.firstBatch[0].options.validator.$jsonSchema;
+    delete schema.properties.demographics.properties.ageBuckets;
+    await db.command( { collMod: 'cases', validator:{ $jsonSchema: schema } } );
+
+    await db.collection('ageBuckets').drop();
+  }
+};

data-serving/scripts/setup-db/schemas/README.md

@@ -1,4 +1,5 @@
 # Mongodb schema validators
 
 This directory contains schema validators and index files for the various collections stored in mongodb.
-These are the _initial_ state of the database: modifications are made via migrations. See the `mongo-migrations` folder for more information.
+These are the _initial_ state of the database: do not make changes here, as they won't make any difference in production!
+Modifications are made via migrations: every new change requires a new migration. See the `migrations` folder for more information.