fix: remove maybe_datum view

typescript/packages/common-memory/README.md

@@ -17,6 +17,14 @@ deno task start
 It will print out service URL endpoint and `file:` URL for the directory where
 memory will be persisted in `.sqlite` files.
 
+## Database Migrations
+
+You can upgrade database to latest version by running following command from the package root
+
+```sh
+deno task migrate ./path/to/db.sqlite
+```
+
 ## Data Model
 
 Memory records are represented as a discrete facts in the shape of

typescript/packages/common-memory/deno.json

@@ -2,7 +2,11 @@
   "name": "@commontools/memory",
   "tasks": {
     "start": "deno run --allow-read --allow-write --allow-net --allow-ffi --allow-env deno.ts",
-    "test": "deno test --allow-read --allow-write --allow-net --allow-ffi --allow-env --no-check"
+    "test": "deno test --allow-read --allow-write --allow-net --allow-ffi --allow-env --no-check",
+    "migrate": {
+      "description": "Performs database migration",
+      "command": "deno run -A ./migrate.ts"
+    }
   },
   "test": {
     "include": [

typescript/packages/common-memory/migrate.ts

@@ -0,0 +1,92 @@
+import {
+  Database,
+  SqliteError,
+  Transaction as DBTransaction,
+} from "jsr:@db/sqlite";
+
+const MIGRATIONS = new URL("./migrations/", import.meta.url);
+
+class Migration {
+  constructor(
+    public db: Database,
+    public id: number,
+    public name: string,
+    public url: URL,
+  ) {}
+
+  execute() {
+    const content = Deno.readFileSync(this.url);
+    this.db.exec(new TextDecoder().decode(content));
+  }
+
+  migrate() {
+    this.execute();
+    this.db.run(
+      `INSERT INTO migration (id, title) VALUES (:id, :title)`,
+      { id: this.id, title: this.name },
+    );
+  }
+}
+
+const migrations = (db: Database): Migration[] => {
+  const migrations = Deno.readDirSync(MIGRATIONS).flatMap(
+    ({ name, isFile }) => {
+      const id = parseInt(name.slice(0, name.indexOf("-")));
+      if (!isFile || isNaN(id)) {
+        return [];
+      } else {
+        return [new Migration(db, id, name, new URL(name, MIGRATIONS))];
+      }
+    },
+  );
+
+  return [...migrations].sort((left, right) => left.id - right.id);
+};
+
+const current = (db: Database) =>
+  db.prepare(
+    `SELECT * FROM migration ORDER BY id DESC LIMIT 1;`,
+  ).get() as { id: number; title: string; time: string };
+
+export const migrate = (db: Database) => {
+  const [setup, ...updates] = migrations(db);
+  // First we run the setup
+  setup.execute();
+  const { time, id, title } = current(db);
+
+  console.log(
+    `🔎 DB was last migrated on ${time} to version ${id} via ${title}`,
+  );
+
+  try {
+    let migration = null;
+    for (migration of updates) {
+      if (migration.id > id) {
+        console.log(`⏭️ Migrating to ${migration.id} using ${migration.name}`);
+        migration.migrate();
+      } else {
+        migration = null;
+      }
+    }
+
+    if (migration) {
+      console.log(`🏁 DB was successfully migrated to version ${migration.id}`);
+    } else {
+      console.log(`✅ DB is already at latest version ${id}`);
+    }
+  } catch (reason) {
+    console.error(`💥 Migration failed`, reason);
+  }
+};
+export const main = (database: string) => {
+  const path = Deno.realPathSync(database);
+  console.log(`💾 Loading ${path}`);
+  const db = new Database(path, {
+    create: false,
+    unsafeConcurrency: true,
+  });
+
+  return db.transaction(migrate)(db);
+};
+
+main(...Deno.args as [string]);

typescript/packages/common-memory/migrations/000-setup-migrations.sql

@@ -0,0 +1,8 @@
+CREATE TABLE IF NOT EXISTS migration (
+  id INTEGER PRIMARY KEY NOT NULL,
+  title TEXT NOT NULL,
+  time TIMESTAMP DEFAULT CURRENT_TIMESTAMP NOT NULL
+);
+
+INSERT OR IGNORE INTO migration (id, title)
+VALUES (0, '000-setup-migrations.sql');

typescript/packages/common-memory/migrations/001-drop-maybe_datum.sql

@@ -0,0 +1,89 @@
+-- Drop indexes
+DROP INDEX memory_the;
+DROP INDEX memory_of;
+DROP INDEX IF EXISTS fact_since;
+
+-- -- Drop views
+DROP VIEW state;
+DROP VIEW IF EXISTS maybe_datum;
+
+-- Archive all tables
+ALTER TABLE datum RENAME TO datum_archive;
+ALTER TABLE fact RENAME TO fact_archive;
+ALTER TABLE memory RENAME TO memory_archive;
+
+-- Create table for storing JSON data.
+-- ⚠️ We need make this NOT NULL because SQLite does not uphold uniqueness on NULL
+CREATE TABLE datum (
+  this TEXT NOT NULL PRIMARY KEY,     -- Merkle reference for this JSON
+  source JSON                         -- Source for this JSON
+);
+
+CREATE TABLE fact (
+  this    TEXT NOT NULL PRIMARY KEY,  -- Merkle reference for { the, of, is, cause }
+  the     TEXT NOT NULL,              -- Kind of a fact e.g. "application/json"
+  of      TEXT NOT NULL,              -- Entity identifier fact is about
+  'is'    TEXT,                       -- Value entity is claimed to have
+  cause   TEXT,                       -- Causal reference to prior fact
+  since   INTEGER NOT NULL,           -- Lamport clock since when this fact was in effect
+  FOREIGN KEY('is') REFERENCES datum(this)
+);
+
+CREATE TABLE memory (
+  the     TEXT NOT NULL,        -- Kind of a fact e.g. "application/json"
+  of      TEXT NOT NULL,        -- Entity identifier fact is about
+  fact    TEXT NOT NULL,          -- Link to the fact,
+  FOREIGN KEY(fact) REFERENCES fact(this),
+  PRIMARY KEY (the, of)         -- Ensure that we have only one fact per entity
+);
+
+-- Create indexes
+CREATE INDEX memory_the ON memory (the); -- Index to filter by "the" field
+CREATE INDEX memory_of ON memory (of);   -- Index to query by "of" field
+CREATE INDEX fact_since ON fact (since); -- Index to query by "since" field
+
+-- Migrate data
+INSERT INTO datum (this, source)
+SELECT this, source
+FROM datum_archive;
+
+-- Insert `NULL` value if not exists already
+INSERT INTO datum (this, source) VALUES ('undefined', NULL);
+
+-- Not sure why but without this complicated query we run into
+-- foreign key constraint while this seems to avoid it yet copy same
+-- amount of rows.
+INSERT INTO fact (this, the, of, 'is', cause, since)
+SELECT fa.this, fa.the, fa.of, fa.'is', fa.cause, fa.since
+FROM fact_archive fa
+LEFT JOIN datum d ON fa.'is' = d.this
+WHERE fa.'is' IS NULL OR d.this IS NOT NULL;
+
+
+INSERT INTO memory (the, of, fact)
+SELECT ma.the, ma.of, ma.fact
+FROM memory_archive ma
+LEFT JOIN fact f ON ma.fact = f.this
+WHERE f.this IS NOT NULL;  -- Include only rows with valid 'fact' references
+
+
+-- Create new 'state' view
+CREATE VIEW state AS
+SELECT
+  memory.the AS the,
+  memory.of AS of,
+  datum.source AS 'is',
+  fact.cause AS cause,
+  memory.fact AS fact,
+  datum.this AS proof,
+  fact.since AS since
+FROM
+  memory
+JOIN
+  fact ON memory.fact = fact.this
+JOIN
+  datum ON datum.this = COALESCE(fact.'is', 'undefined');
+
+DROP TABLE memory_archive;
+DROP TABLE fact_archive;
+DROP TABLE datum_archive;

typescript/packages/common-memory/space.ts

@@ -44,23 +44,25 @@ export const PREPARE = `
 BEGIN TRANSACTION;
 
 -- Create table for storing JSON data.
+-- ⚠️ We need make this NOT NULL because SQLite does not uphold uniqueness on NULL
 CREATE TABLE IF NOT EXISTS datum (
-  this    TEXT PRIMARY KEY,     -- Merkle reference for this JSON
-  source  JSON NOT NULL         -- Source for this JSON
+  this TEXT NOT NULL PRIMARY KEY,     -- Merkle reference for this JSON
+  source JSON                         -- Source for this JSON
 );
 
-CREATE VIEW IF NOT EXISTS maybe_datum AS
-SELECT * FROM datum
-UNION ALL
-SELECT NULL AS this, NULL AS source;
+-- We create special record to represent undefined which does not exist in JSON.
+-- This allows us to join fact with datum table and cover retractions where
+-- fact.is is set to NULL
+INSERT OR IGNORE INTO datum (this, source) VALUES ('undefined', NULL);
+
 
 CREATE TABLE IF NOT EXISTS fact (
-  this    TEXT PRIMARY KEY,     -- Merkle reference for { the, of, is, cause }
-  the     TEXT NOT NULL,        -- Kind of a fact e.g. "application/json"
-  of      TEXT NOT NULL,        -- Entity identifier fact is about
-  'is'    TEXT,                 -- Value entity is claimed to have
-  cause   TEXT,                 -- Causal reference to prior fact
-  since   INTEGER NOT NULL,     -- Lamport clock since when this fact was in effect
+  this    TEXT NOT NULL PRIMARY KEY,  -- Merkle reference for { the, of, is, cause }
+  the     TEXT NOT NULL,              -- Kind of a fact e.g. "application/json"
+  of      TEXT NOT NULL,              -- Entity identifier fact is about
+  'is'    TEXT,                       -- Value entity is claimed to have
+  cause   TEXT,                       -- Causal reference to prior fact
+  since   INTEGER NOT NULL,           -- Lamport clock since when this fact was in effect
   FOREIGN KEY('is') REFERENCES datum(this)
 );
 
@@ -74,22 +76,33 @@ CREATE TABLE IF NOT EXISTS memory (
 
 CREATE INDEX IF NOT EXISTS memory_the ON memory (the); -- Index to filter by "the" field
 CREATE INDEX IF NOT EXISTS memory_of ON memory (of);   -- Index to query by "of" field
+CREATE INDEX IF NOT EXISTS fact_since ON fact (since); -- Index to query by "since" field
 
+-- Create the updated 'state' view
 CREATE VIEW IF NOT EXISTS state AS
 SELECT
-  memory.the as the,
-  memory.of as of,
-  maybe_datum.source as 'is',
-  fact.cause as cause,
-  memory.fact as fact,
-  maybe_datum.this as proof,
-  fact.since as since
+  memory.the AS the,
+  memory.of AS of,
+  datum.source AS 'is',
+  fact.cause AS cause,
+  memory.fact AS fact,
+  datum.this AS proof,
+  fact.since AS since
 FROM
   memory
+-- We use inner join because we memory.fact can not be NULL and as foreign
+-- key into fact.this which is also primary key. This guarantees that we will
+-- not have any memory record with corresponding fact record
 JOIN
   fact ON memory.fact = fact.this
+-- We use inner join here because fact.is || 'undefined' is guaranteed to have
+-- corresponding record in datum through a foreign key constraint and inner
+-- joins are generally more efficient that left joins.
+-- ⚠️ Also note that we use COALESCE operator to use 'undefined' in case where
+-- there fact.is NULL (retractions), which is important because SQLite never
+-- matches over fact.is = NULL.
 JOIN
-  maybe_datum ON fact.'is' = maybe_datum.this OR (fact.'is' IS NULL AND maybe_datum.this IS NULL);
+  datum ON datum.this = COALESCE(fact.'is', 'undefined');
 
 COMMIT;
 `;