openehr-mysql

openEHR persistence for MySQL 8.4 — the schema dialect.

Conformance level: Schema#

This crate emits DDL for the shared openEHR schema, and a MySQL 8.4 server has executed it: five tables, seven indexes, idempotent on re-application, and both append-only tables refusing UPDATE and DELETE with a row present and intact afterwards.

../openehr-store/scripts/verify-schema.sh mysql

That run is why two of this crate's decisions look unlike the others. MySQL declares its indexes inside CREATE TABLE, because it accepts CREATE TABLE IF NOT EXISTS and rejects CREATE INDEX IF NOT EXISTS (A-13 — before the fix, install() created every table and then failed at the first index). And its triggers are dropped before being created, because MySQL 8 has neither CREATE TRIGGER IF NOT EXISTS nor CREATE OR REPLACE TRIGGER.

It does not contain a store. There is no driver dependency, no connection handling, and no implementation of Store. Schema level means the database accepts the schema, not that this crate can talk to it.

See openehr-store/spec/conformance.md for what each level means and why they are stated this bluntly.

use openehr_mysql::MysqlDialect;
use openehr_store::ddl_script;

println!("{}", ddl_script(&MysqlDialect));

What this crate owns#

Four things: type spellings, identifier quoting, placeholder style, and how the engine enforces append-only. Everything else — which tables exist, which columns, which indexes, the projection from openEHR objects onto rows, the commit rules, the conformance suite — lives in openehr-store and is shared by all five engines.

That boundary is deliberate. The sibling FHIR monorepo in this repository gave each of six ports a full copy of the DDL generator, and one of the copies spent the fork's whole life emitting another engine's types (F-08). A dialect that owns only spellings cannot do that, and openehr-sqlite/tests/dialects.rs compares all five to make sure.

MySQL 8.4 specifics#

Decision	Why
`VARCHAR(n)` with a mandatory length	InnoDB cannot index an unbounded column, and every identifier column in this schema is a key or part of one.
`JSON`, the native type	MySQL validates it on write, which catches a malformed document at the boundary rather than at read time.
`DATETIME(6)` for derived instants	Microseconds is MySQL's maximum. openEHR permits finer fractional seconds in the lexical form — which is why that form is stored separately and authoritatively.
`TINYINT(1)` for booleans	MySQL has no boolean type; this is the conventional spelling and what every driver maps to `bool`.
No append-only trigger	MySQL triggers cannot raise a clean error before 8.0's `SIGNAL`, and this crate has not been run against a server to confirm the form. Left undone and stated, rather than emitted untested.

Every instant is stored twice, and that is the point#

openEHR times are ISO 8601 strings with deliberate partial precision: 2024-05 is a date known to the month, and it is not 2024-05-01. A native timestamp column silently completes it — fabricating a clinical fact — and normalises the lexical form, breaking round-trip fidelity.

So each time occupies …_text (authoritative, exact) and …_utc (derived, nullable, for ordering). The derived column is NULL whenever the instant is not established, which is the same answer the library gives, so SQL and Rust cannot disagree about one record.

Testing#

cargo test

The tests are golden: they assert the SQL this crate emits, including assertions that it is not another engine's SQL.

Licence#

MIT OR Apache-2.0.