Remove automatic generated property columns

The columns could only be text, since a typed column makes Cypher writes
fail on values of another type. Leave typed columns and views to the
database administrator instead, and document how to set them up.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -42,8 +42,7 @@ graph as a schema of the same name, with one table per label.
 - **Databases are AGE graphs.** Every AGE graph shows up as a Neo4j database, and
   `:use <name>` switches between them. A graph named `neo4j` is created on first start
   (`PEO_DEFAULT_GRAPH`). `CREATE DATABASE x` and `DROP DATABASE x` on the `system`
-  database call `create_graph` / `drop_graph`; AGE requires names of at least 3 characters,
-  and `peo` is reserved for the schema holding peo's SQL helpers.
+  database call `create_graph` / `drop_graph`; AGE requires names of at least 3 characters.
 - **Queries** are sent to AGE as `SELECT * FROM cypher('<graph>', $$ <query> $$) AS (...)`.
   The bridge works out the result columns from the final `RETURN` clause and inlines
   query parameters as Cypher literals.
@@ -60,31 +59,30 @@ graph as a schema of the same name, with one table per label.
 ## Querying the graph from SQL
 
 AGE stores each node label and relationship type as a table in the graph's schema,
-with all properties in one `agtype` column, `properties`. peo adds a generated
-column for every property key it finds, so you can use plain SQL:
+with all properties in one `agtype` column, `properties`; `properties ->> 'key'::text`
+returns a property as text. For typed columns, add them yourself, either as a view or
+as a generated column:
 
 ```sql
-SELECT name, age FROM neo4j."Person" WHERE name LIKE 'A%';
-CREATE INDEX ON neo4j."Person" (name);
+CREATE VIEW neo4j.people AS
+    SELECT id, properties ->> 'name'::text AS name, (properties ->> 'age'::text)::bigint AS age
+    FROM neo4j."Person";
+
+ALTER TABLE neo4j."Person"
+    ADD COLUMN age bigint GENERATED ALWAYS AS ((properties ->> 'age'::text)::bigint) STORED;
 ```
 
-AGE's Cypher writes do not fire PostgreSQL triggers, so new keys cannot be caught
-the moment they are written. Instead the bridge calls
-`CALL peo.sync_property_columns()` every few seconds
-(`PEO_PROPERTY_COLUMNS_INTERVAL`), which you can also run yourself. It only scans
-tables that had inserts or updates since its previous run, and adds all new keys of a
-table with a single `ALTER TABLE`. Once a column exists, PostgreSQL keeps it in step
-with every `CREATE`, `MERGE`, `SET` and `REMOVE`.
+PostgreSQL keeps generated columns up to date on every Cypher `CREATE`, `MERGE`, `SET`
+and `REMOVE`, and they can be indexed. Some things to keep in mind:
 
-- Columns are `text`, the same as `properties->>'key'`: one key can hold values of
-  different types in different rows, and a failing cast would make writes fail. Cast
-  in your query, for example `age::int`. Lists and maps come out as JSON text.
-- Keys that clash with an existing column (`id`, `properties`, `start_id`, `end_id`)
-  get no column. Use `properties->>'id'` for those.
-- Adding a column rewrites the table, which locks it for the duration. On a large
-  table this blocks writes to that label for a while, but only once per new key.
-- AGE does not allow dropping columns from label tables, so a column stays after its
-  key disappears from the data.
+- A value that does not fit the column's type makes the Cypher write fail: with the
+  column above, `CREATE (:Person {age: 'old'})` is rejected. A view only fails when it
+  is read.
+- AGE does not allow dropping columns from its label tables, so a generated column
+  cannot be removed again.
+- Adding a stored generated column rewrites the table and locks it while doing so.
+- AGE has no date or time types, so store those as ISO 8601 strings and cast them in
+  SQL.
 
 ## Configuration
 
@@ -96,8 +94,6 @@ with every `CREATE`, `MERGE`, `SET` and `REMOVE`.
 | `PEO_ADVERTISED_BOLT_PORT` | `7687` | Bolt port advertised to the browser; set it when you publish 7687 on another host port. |
 | `PEO_ADVERTISED_HOST` | `localhost` | Host reported in `SHOW DATABASES` and to clients that do not send a routing address. |
 | `PEO_LOG_LEVEL` | `INFO` | `DEBUG` logs every generated SQL statement. |
-| `PEO_PROPERTY_COLUMNS` | `true` | Set to `false` to stop adding generated property columns. |
-| `PEO_PROPERTY_COLUMNS_INTERVAL` | `5` | Seconds between checks for new property keys. |
 | `PGADMIN_DEFAULT_EMAIL` | `admin@example.com` | pgAdmin login, created on first start. |
 | `PGADMIN_DEFAULT_PASSWORD` | `$POSTGRES_PASSWORD` | pgAdmin login password, set on first start. |
 | `PEO_PGADMIN` | `true` | Set to `false` to not start pgAdmin. |