SQL: PostgreSQL, MySQL & SQLite

The vantage-sql crate provides persistence implementations for three SQL databases via sqlx. All three share the same architecture — CBOR-based type systems, expression engine, query builder, and full TableSource implementation — but each has vendor-specific behaviour around type affinity, quoting, and parameter binding.

Backends

What they implement

All three implement the full trait stack:

• DataSource — marker
• ExprDataSource — parametric SQL execution with CBOR values
• SelectableDataSource — query builder with JOINs, CTEs, window functions
• TableSource — full CRUD, columns, conditions, aggregates
• TableQuerySource — table definition → full query

CBOR value representation

All SQL backends use CBOR (ciborium::Value) as their internal value type — not JSON. This preserves type fidelity that JSON loses:

• Integer vs Float — JSON’s 42 is ambiguous; CBOR distinguishes Integer(42) from Float(42.0)
• Binary data — CBOR has native byte arrays; JSON would need base64 encoding
• Precise decimals — stored as tagged CBOR values, not lossy floats

Values are converted to CBOR on write (via the type system’s to_cbor()) and read back as untyped CBOR (via from_cbor()). The type markers from vantage_type_system! ensure correct binding — integers bind as i64, text as &str, booleans as bool.

Type conversion reference

Each database handles Rust types differently depending on the column type. See the Type Conversions reference for detailed round-trip tables covering:

• Chrono types — NaiveDate, NaiveTime, NaiveDateTime, DateTime<Utc>, DateTime<FixedOffset>
• Numeric types — Decimal, i64, f64
• Exact vs lossy vs truncated behaviour per column type
• Cross-type coercion rules and error cases