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Custom type mapping

sqlpp23-ddl2cpp natively knows how to map many SQL types to C++ types. However, if you want, you can specify custom mappings using several mechanisms as documented below.

Custom mappings can use the types provided by sqlpp23:

  • ::sqlpp::blob: Blob (binary large object).
  • ::sqlpp::boolean: Boolean.
  • ::sqlpp::date: Date (year + month + day of month).
  • ::sqlpp::floating_point: Floating-point.
  • ::sqlpp::integral: Integral (integer) data type. Booleans are not considered an integral type.
  • ::sqlpp::serial: Integral (integer) value with auto-increment. Always has a default value, so it cannot be NULL.
  • ::sqlpp::text: Text.
  • ::sqlpp::time: Time of day.
  • ::sqlpp::timestamp: Tmestamp (date + time).

In addition, sqlpp23 supports user-defined C++ types as column data types (see Custom types).

Mapping priorities

All mechanisms can be used in parallel. They are applied in the following order:

  • sqlpp23 default mapping (lowest priority)
  • CSV: SQL type -> C++ type
  • CSV: column name -> C++ type
  • CSV: table.column name -> C++ type
  • CSV: schema.table.column -> C++ type
  • comment annotations of any kind (these must not contradict each other)

CSV file

The --path-to-custom-type-mapping command-line option (see Command-line options) specifies the path to a CSV file. Each line contains three comma-separated fields

  1. row_type: This can be either type or column.
  2. entity: If row_type == type, this is an SQL type. Otherwise this is a column name with or without table qualification, e.g. bar or tab_foo.bar.
  3. cpp_type: This is the C++ type to represent the specified entity, e.g. ::sqlpp::integral or ::some::uuid.

For instance:

type, SPECIAL INT, ::sqlpp::integral
type, UUID, ::some::uuid
column, first_name, ::my_own::string
column, tab_employee.first_name, ::sqlpp::text
column, internal.tab_employee.first_name, ::corp::string

Inline SQL comment

Place a -- ... cpp_type:<type> ... comment on the line immediately before the column definition. The annotation can appear anywhere in the comment; surrounding text is ignored:

CREATE TABLE tab_point (
    -- cpp_type:point_id
    id bigint AUTO_INCREMENT PRIMARY KEY,
    -- this column holds cpp_type:XCoord (horizontal axis)
    x bigint NOT NULL,
    -- cpp_type:YCoord
    y bigint NOT NULL
);

This option works with all backends.

MySQL column COMMENT clause

When using the MySQL or MariaDB backend, the annotation can be embedded in the column's COMMENT attribute. The cpp_type: keyword is extracted from the comment string wherever it appears:

CREATE TABLE tab_foo (
    `id`     bigint NOT NULL AUTO_INCREMENT,
    `int_n`  int    DEFAULT NULL COMMENT 'cpp_type:test::my_int',
    PRIMARY KEY (`id`)
);

PostgreSQL COMMENT ON COLUMN

When using the PostgreSQL backend, annotations can be embedded in COMMENT ON COLUMN statements. The cpp_type: keyword is extracted from the comment string wherever it appears:

COMMENT ON COLUMN public.tab_point.x IS 'x coordinate cpp_type:XCoord (horizontal axis)';
COMMENT ON COLUMN public.tab_point.y IS 'cpp_type:YCoord';

Use --strip-sql-schema together with this option so that schema-qualified table names (e.g. public.tab_point) are resolved correctly against the generated table definitions (see sqlpp23-ddl2cpp).

Include headers for custom C++ types

Use the --custom-directives option to add custom #include or import lines to the generated file.

< Index