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Type mapping reference

Mapping is dialect-aware: sqlparser parses dialect-specific keywords, and this tool normalizes the result to one of Loco's canonical type names. Length and precision arguments are parsed (and visible in the IR) but are not used for type selection — Loco's type names don't carry them.

Full mapping

SQL type Loco type Notes
UUID uuid
BOOL, BOOLEAN bool
TINYINT(1) bool MySQL convention.
TINYINT small_int Without (1) — see below.
SMALLINT, INT2, MEDIUMINT small_int MEDIUMINT is 24-bit in MySQL but maps here for closeness — see Edge cases.
INT, INT4, INTEGER, SERIAL int Postgres SERIAL is auto-increment; the auto-increment is implicit in Loco.
BIGINT, INT8, BIGSERIAL big_int
SMALLINT UNSIGNED small_unsigned MySQL only.
INT UNSIGNED unsigned MySQL only.
BIGINT UNSIGNED big_unsigned MySQL only.
REAL, FLOAT4 float 32-bit.
DOUBLE, DOUBLE PRECISION, FLOAT8 double 64-bit.
FLOAT (no precision) double See Edge cases.
NUMERIC, NUMERIC(p,s) decimal Precision/scale parsed but discarded.
DECIMAL, DECIMAL(p,s) decimal
MONEY money Postgres.
CHAR, CHARACTER string
VARCHAR, VARCHAR(n) string Length parsed but discarded.
NVARCHAR, CHARACTER VARYING string
TEXT, MEDIUMTEXT, LONGTEXT, CLOB text
DATE date
TIME string Loco has no time type — falls back.
TIMESTAMP, DATETIME date_time
TIMESTAMPTZ, TIMESTAMP WITH TIME ZONE tstz Postgres.
JSON json
JSONB jsonb Postgres.
<type>[], ARRAY array Postgres array; element type is currently dropped.
BYTEA blob Postgres.
BLOB, MEDIUMBLOB, LONGBLOB blob MySQL.
BINARY(n) binary_len Length carried as IR arg but Loco's binary_len is fixed.
VARBINARY(n) var_binary
anything else string Emits a stderr warning.

Suffixes

After the type name, one or both of these suffixes may appear (in order, no separator):

  • ! — column is NOT NULL or has inline PRIMARY KEY.
  • ^ — column has inline UNIQUE, or appears as the only column in a table-level UNIQUE (col) constraint.

A NOT NULL UNIQUE column emits name:type!^.

Foreign-key columns (those carrying a REFERENCES clause) never get suffixes — Loco's references template owns nullability and uniqueness for those fields. See foreign-keys.md.

Unsigned promotion

For MySQL columns marked UNSIGNED, the integer type is promoted:

Base Becomes
small_int small_unsigned
int unsigned
big_int big_unsigned
anything else unchanged (UNSIGNED REAL etc. stay float)

The promotion only applies to the three integer types Loco offers an unsigned counterpart for. TINYINT(1) UNSIGNED is still bool (the (1) rule wins before the unsigned promotion).

Edge cases

MEDIUMINT truncation

MySQL MEDIUMINT is 24-bit (range ~±8 million). Loco has no medium_int, so this tool maps it to small_int (16-bit). Values outside ±32767 won't fit. If you have MEDIUMINT columns with real-world values above the SMALLINT range, consider editing the output to int (32-bit) by hand, or change your schema to INT to avoid the surprise.

FLOAT precision rules

Per the SQL standard, FLOAT(p) with p ≤ 24 is single-precision and FLOAT(p) with p ≥ 25 is double-precision. This tool maps any FLOAT to double regardless of precision. If you specifically need 32-bit, use REAL or FLOAT4.

BINARY(n) vs VARBINARY(n)

Loco's binary_len is a fixed-length binary type; var_binary is variable. The length argument is parsed and held in the IR but isn't currently used to select a different Loco type. If your BINARY(16) column needs to be exactly 16 bytes, edit the migration after scaffolding.

Postgres arrays

int[] and varchar[] both map to array (the element type is dropped). Loco's array support is broad enough that the element type isn't carried in the scaffold field syntax.

Unknown types

If sqlparser parses a type but this tool doesn't have an explicit rule for it (e.g., dialect-specific extensions), the column is emitted as <col>:string with a warning:

warn: unknown SQL type 'WIDGET', mapped to string (column 't.q')

This is a deliberate "don't crash on stray dialects" fallback. Edit the output if string is wrong.

Source of truth

Loco's canonical type names are documented at loco.rs/docs/the-app/models/. This tool tracks the names current as of the spec's 2026-05-04 revision. Older Loco versions used different names (ts instead of tstz, bigint instead of big_int, etc.) — the design spec records the migration.