Capabilities

Each capability lists the API that provides it and the MPA rules that define it. The same list is in docs/mpa.json for tools.

Capability	What it does	API	Rules
typed-views	Declare the shape of nested data with Rust structs deriving View	#[derive(View)] #[view(table, key)]	MPA-CORE-1, MPA-VIEW-1
batched-loading	Load a view with one batched query per relationship, never one per row	mabat::load	MPA-PLAN-1
multiple-databases	PostgreSQL, MySQL 8+ and SQLite, chosen by features and by the connection	features: postgres, mysql, sqlite #[view(databases)]	MPA-DB-1, MPA-DB-2
embedded-values	Structs stored in columns of the containing view, generic or not	#[view(embedded)] #[view(embed(prefix))] mabat::GenericColumn	MPA-VIEW-3, MPA-VIEW-4, MPA-VIEW-7
enums-with-data	Rust enums with data, stored in columns or in a table per variant, decoded strictly	#[view(tag, strategy, lenient)] #[view(tag_value)]	MPA-SUM-1, MPA-SUM-2, MPA-SUM-3, MPA-SUM-4
json-columns	Columns decoded and written as JSON with serde	#[view(json)]	MPA-VIEW-6
to-one-references	References to other views by foreign key, owned, boxed, shared or into a graph	#[view(to_one(fk))] Box<T>	MPA-VIEW-8
collections	To-many collections, ordered, placed by index, or as maps	#[view(child(fk, order_by, index, key))]	MPA-VIEW-9, MPA-VIEW-10
many-to-many	Collections through a link table	#[view(child(through, target))]	MPA-VIEW-9
recursive-views	Trees and chains of parents by depth-limited levels or one WITH RECURSIVE query	#[view(child(depth))] #[view(child(recursive = "cte"))] #[view(to_one(depth))] #[view(to_one(recursive = "cte"))]	MPA-PLAN-4, MPA-LOAD-12, MPA-VIEW-8
shared-values	Arc values decoded once per entity and shared	Arc<T>	MPA-LOAD-13
graphs	Cyclic data as a Graph of entities with typed references	Ref<T> Load::graph Graph	MPA-LOAD-14
filters-and-paging	Filters, ordering, paging and counting of the root rows	mabat::filter::col Load::filter Load::order_by Load::limit Load::offset Load::count	MPA-LOAD-4, MPA-LOAD-5, MPA-LOAD-6
nested-arguments	Filter, order and page the elements of a collection per parent, in one query	Load::nested Nested	MPA-LOAD-9, MPA-LOAD-10
streaming	Load many values a batch at a time, as a stream, holding one batch in memory	Load::stream Load::json_stream Load::batch_size	MPA-LOAD-15, MPA-LOAD-16, MPA-LOAD-17, MPA-LOAD-18
concurrent-loads	Run the queries of each level concurrently on a pool, optionally in one snapshot	Pooled::snapshot Pooled::read_committed	MPA-LOAD-11
sql-overrides	Replace any query of a view with tuned SQL from a file, checked at startup	Mabat::builder overrides_dir overrides_sql -- mabat: query <name>	MPA-OVR-1, MPA-OVR-2, MPA-OVR-3, MPA-OVR-4, MPA-OVR-5
shadow-mode	Run an override next to the generated query and log differences	shadow Mabat::shadow_stats	MPA-OVR-6
override-reload	Reload override files without restarting	Mabat::reload	MPA-OVR-7
schema-snapshots	A snapshot of the database’s schema, its drift, and views checked against it without a database	mabat schema mabat::schema::snapshot mabat check --snapshot Manifest::check_snapshot mabat_check::build	MPA-SCH-1, MPA-SCH-2, MPA-SCH-3, MPA-SCH-4, MPA-SCH-5, MPA-SCH-6, MPA-SCH-7
dba-tooling	A manifest of the views and the mabat command line tool: check, explain, scaffold	Builder::manifest mabat check mabat explain mabat scaffold	MPA-OVR-8
report-queries	Reports: root SQL with named parameters and computed fields	Load::sql Load::bind #[view(computed)]	MPA-LOAD-19, MPA-VIEW-13, MPA-OVR-3
tracing	tracing spans for each operation, query and statement, with names, rows and times	tracing RUST_LOG=mabat=debug	MPA-DB-6
json-loading	Load views as JSON, whole or a selection of their fields	Load::json Load::select Selection::parse Load::graph_json	MPA-JSON-1, MPA-JSON-3, MPA-JSON-4, MPA-JSON-5, MPA-JSON-7
graphql	A GraphQL schema generated from views, each root field one load	mabat_graphql::schema	MPA-GQL-1, MPA-GQL-2, MPA-GQL-3, MPA-GQL-4
save-aggregates	Save a value and everything it owns, creating or replacing rows by key	mabat::save	MPA-WRITE-1, MPA-WRITE-3, MPA-WRITE-4, MPA-WRITE-5, MPA-WRITE-6
save-changes	Save only what changed between two values of an aggregate	mabat::save_changes	MPA-WRITE-8
optimistic-locking	Version columns that make stale writes fail	#[view(version)] Error::Conflict	MPA-WRITE-9, MPA-WRITE-10
save-many	Save many values with statements per table and level, not per row	mabat::save_all	MPA-WRITE-19
save-graphs	Save every entity of a graph, ordered by its references, cycles included	mabat::save_graph Graph::new Graph::insert	MPA-WRITE-14, MPA-WRITE-15, MPA-WRITE-16, MPA-WRITE-17, MPA-WRITE-18
save-graph-changes	Save only the entities of a graph that were inserted or handed out by get_mut	mabat::save_graph_changes Graph::is_changed	MPA-WRITE-20
generated-keys	Keys generated by the database on insert, written back into the value	#[view(generated)] mabat::save	MPA-WRITE-13, MPA-WRITE-10
delete-aggregates	Delete a value and everything it owns	mabat::delete	MPA-WRITE-7

Not supported

• MPA-NOT-3 A unit of work that collects writes and flushes them later (MPA-WRITE-1).
• MPA-NOT-4 Lazy loading: everything a view declares is loaded by the load, or selected (section 8).
• MPA-NOT-5 Writes through overrides, and override SQL for writes.
• MPA-NOT-6 Filtering by columns of embedded structs in filter, nested or GraphQL where.
• MPA-NOT-7 Arguments on map collections in GraphQL, and GraphQL mutations.
• MPA-NOT-8 Pipelining queries on one connection.
• MPA-NOT-9 Schema generation or migrations: views describe existing tables.