Add migration to add sequence numbers to documents (#64)

Author: Greg Soltis

firebase-firestore/src/main/java/com/google/firebase/firestore/local/SQLiteSchema.java

@@ -38,7 +38,9 @@ class SQLiteSchema {
    * The version of the schema. Increase this by one for each migration added to runMigrations
    * below.
    */
-  static final int VERSION = (Persistence.INDEXING_SUPPORT_ENABLED) ? 7 : 6;
+  static final int VERSION = 7;
+  // Remove this constant and increment VERSION to enable indexing support
+  static final int INDEXING_SUPPORT_VERSION = VERSION + 1;
 
   private final SQLiteDatabase db;
 
@@ -99,6 +101,10 @@ void runMigrations(int fromVersion, int toVersion) {
     }
 
     if (fromVersion < 7 && toVersion >= 7) {
+      ensureSequenceNumbers();
+    }
+
+    if (fromVersion < INDEXING_SUPPORT_VERSION && toVersion >= INDEXING_SUPPORT_VERSION) {
       Preconditions.checkState(Persistence.INDEXING_SUPPORT_ENABLED);
       createLocalDocumentsCollectionIndex();
     }
@@ -245,4 +251,34 @@ private void addTargetCount() {
   private void addSequenceNumber() {
     db.execSQL("ALTER TABLE target_documents ADD COLUMN sequence_number INTEGER");
   }
+
+  /**
+   * Ensures that each entry in the remote document cache has a corresponding sentinel row. Any
+   * entries that lack a sentinel row are given one with the sequence number set to the highest
+   * recorded sequence number from the target metadata.
+   */
+  private void ensureSequenceNumbers() {
+    // Get the current highest sequence number
+    SQLitePersistence.Query sequenceNumberQuery =
+        new SQLitePersistence.Query(
+            db, "SELECT highest_listen_sequence_number FROM target_globals LIMIT 1");
+    Long boxedSequenceNumber = sequenceNumberQuery.firstValue(c -> c.getLong(0));
+    hardAssert(boxedSequenceNumber != null, "Missing highest sequence number");
+
+    long sequenceNumber = boxedSequenceNumber;
+    SQLiteStatement tagDocument =
+        db.compileStatement(
+            "INSERT INTO target_documents (target_id, path, sequence_number) VALUES (0, ?, ?)");
+    SQLitePersistence.Query untaggedDocumentsQuery =
+        new SQLitePersistence.Query(
+            db,
+            "SELECT RD.path FROM remote_documents AS RD WHERE NOT EXISTS (SELECT TD.path FROM target_documents AS TD WHERE RD.path = TD.path AND TD.target_id = 0)");
+    untaggedDocumentsQuery.forEach(
+        row -> {
+          tagDocument.clearBindings();
+          tagDocument.bindString(1, row.getString(0));
+          tagDocument.bindLong(2, sequenceNumber);
+          hardAssert(tagDocument.executeInsert() != -1, "Failed to insert a sentinel row");
+        });
+  }
 }

firebase-firestore/src/test/java/com/google/firebase/firestore/local/SQLiteSchemaTest.java

@@ -189,6 +189,49 @@ private void addMutationBatch(SQLiteDatabase db, int batchId, String uid, String
         new Object[] {uid, batchId, write.build().toByteArray()});
   }
 
+  @Test
+  public void addsSentinelRows() {
+    schema.runMigrations(0, 6);
+
+    long oldSequenceNumber = 1;
+    // Set the highest sequence number to this value so that untagged documents
+    // will pick up this value.
+    long newSequenceNumber = 2;
+    db.execSQL(
+        "UPDATE target_globals SET highest_listen_sequence_number = ?",
+        new Object[] {newSequenceNumber});
+
+    // Set up some documents (we only need the keys)
+    // For the odd ones, add sentinel rows.
+    for (int i = 0; i < 10; i++) {
+      String path = "docs/doc_" + i;
+      db.execSQL("INSERT INTO remote_documents (path) VALUES (?)", new String[] {path});
+      if (i % 2 == 1) {
+        db.execSQL(
+            "INSERT INTO target_documents (target_id, path, sequence_number) VALUES (0, ?, ?)",
+            new Object[] {path, oldSequenceNumber});
+      }
+    }
+
+    schema.runMigrations(6, 7);
+
+    // Verify.
+    new SQLitePersistence.Query(
+            db, "SELECT path, sequence_number FROM target_documents WHERE target_id = 0")
+        .forEach(
+            row -> {
+              String path = row.getString(0);
+              long sequenceNumber = row.getLong(1);
+
+              int docNum = Integer.parseInt(path.split("_")[1]);
+              // The even documents were missing sequence numbers, they should now be filled in
+              // to have the new sequence number. The odd documents should have their
+              // sequence number unchanged, and so be the old value.
+              long expected = docNum % 2 == 1 ? oldSequenceNumber : newSequenceNumber;
+              assertEquals(expected, sequenceNumber);
+            });
+  }
+
   private void assertNoResultsForQuery(String query, String[] args) {
     Cursor cursor = null;
     try {