serramatutu commented on code in PR #4694:
URL: https://github.com/apache/arrow-adbc/pull/4694#discussion_r3967216292
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c/include/arrow-adbc/adbc.h:
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@@ -1087,6 +1093,590 @@ const struct AdbcError* AdbcErrorFromArrayStream(struct
ArrowArrayStream* stream
/// @}
+/// \defgroup adbc-statement-metadata-collection Metadata Collections
+///
+/// Fetch (catalog) metadata from the database. On a statement, set
+/// ADBC_METADATA_COLLECTION to one of the collection names below, and set any
+/// filters via the options defined below. (There are driver/vendor-specific
+/// collections and filters as well.) Then call AdbcStatementExecuteQuery or
+/// AdbcStatementExecuteSchema. The result is an Arrow dataset with a schema
+/// defined by the collection. For example, a client may request a list of
+/// tables in the database, or a list of supported data types.
+///
+/// All drivers must implement a collection called "meta" (which is aliased to
+/// NULL and blank string) that defines the available collections. See
+/// ADBC_METADATA_COLLECTION_META.
+///
+/// Drivers may also implement AdbcStatementRequestSchema to (1) request
+/// different data types and (2) drop fields from the result. Drivers are not
+/// required to support this, and are not required to support other changes
+/// like reordering collection fields. Drivers are encouraged to use this to
+/// give applications flexibility over output type and shape (e.g. reducing
+/// memory pressure by run-end-encoding or dictionary-encoding primary key
+/// columns; optimizing queries by using simpler queries and eliminating joins
+/// if the application drops certain columns). Unless requested, however,
+/// drivers should return the type specified below and not substitute a
+/// logically equivalent type (e.g. utf8 below should be a string array by
+/// default, and not a utf8view or large string or other array).
+///
+/// Drivers may add more fields at the end of standard schemas to reflect
+/// vendor-specific metadata. Applications must access these by name or using
+/// an offset from the end of the schema and cannot assume that the index of
+/// the field will remain stable. Hence, it is discouraged to access these
+/// fields by ordinal as this is brittle. Drivers must add the fields at the
+/// end and must prefix field names with the vendor/driver name to
+/// differentiate them (e.g. 'POSTGRESQL:owner', not just 'owner').
+///
+/// Similarly, future standard revisions may add more fields to existing
+/// standard schemas. Applications must not assume the number of fields is
+/// fixed.
+///
+/// Drivers may implement collections beyond those defined by ADBC, but must
+/// use a vendor-specific prefix (e.g. `postgresql.`) to avoid conflicts with
+/// future standardized collections. Drivers must not use the `adbc.` prefix.
+///
+/// Drivers may not necessarily accept filter options or other options before
+/// the collection name option is set.
+///
+/// This is intended to replace AdbcConnectionGetObjects, but both APIs
+/// will be supported for the time being. A driver that implements either
+/// API should implement both APIs. AdbcConnectionGetObjects may be
+/// deprecated in a future revision.
+///
+/// \since ADBC API revision 1.2.0
+///
+/// @{
+
+/// \brief Prepare to fetch a metadata collection.
+///
+/// The type is char*.
+#define ADBC_METADATA_COLLECTION "adbc.metadata.collection"
+
+/// \brief Filter the collection on the literal catalog name.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_CATALOG "adbc.metadata.filter.catalog"
+
+/// \brief Filter the collection on the catalog name, matching a search
+/// pattern.
+///
+/// If both this and ADBC_METADATA_FILTER_CATALOG are set, then the last set
+/// option wins.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_PATTERN_CATALOG
"adbc.metadata.filter_pattern.catalog"
+
+/// \brief Filter the collection on the literal schema name.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_DB_SCHEMA "adbc.metadata.filter.schema"
+
+/// \brief Filter the collection on the schema name, matching a search
+/// pattern.
+///
+/// If both this and ADBC_METADATA_FILTER_DB_SCHEMA are set, then the last set
+/// option wins.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_PATTERN_DB_SCHEMA
"adbc.metadata.filter_pattern.schema"
+
+/// \brief Filter the collection on the literal table name.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_TABLE "adbc.metadata.filter.table"
+
+/// \brief Filter the collection on the table name, matching a search pattern.
+///
+/// If both this and ADBC_METADATA_FILTER_TABLE are set, then the last set
+/// option wins.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_PATTERN_TABLE "adbc.metadata.filter_pattern.table"
+
+/// \brief Filter the collection on the literal column name.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_COLUMN "adbc.metadata.filter.column"
+
+/// \brief Filter the collection on the column name, matching a search
+/// pattern.
+///
+/// If both this and ADBC_METADATA_FILTER_COLUMN are set, then the last set
+/// option wins.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_PATTERN_COLUMN
"adbc.metadata.filter_pattern.column"
+
+/// \brief Filter the collection on the table types.
+///
+/// Separator: comma (',').
+/// The type is char*.
+#define ADBC_METADATA_FILTER_TABLE_TYPES "adbc.metadata.filter.table_types"
+
+/// \brief Filter the collection on the literal catalog name of the foreign
+/// key.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_FOREIGN_CATALOG
"adbc.metadata.filter.foreign_catalog"
+
+/// \brief Filter the collection on the literal schema name of the foreign
+/// key.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_FOREIGN_DB_SCHEMA
"adbc.metadata.filter.foreign_schema"
+
+/// \brief Filter the collection on the literal catalog name of the foreign
+/// key.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_FOREIGN_TABLE "adbc.metadata.filter.foreign_table"
+
+/// \brief Filter the collection on the literal constraint name.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_CONSTRAINT "adbc.metadata.filter.constraint"
+
+/// \brief Filter the collection on the constraint name, matching a search
+/// pattern.
+///
+/// If both this and ADBC_METADATA_FILTER_CONSTRAINT are set, then the last set
+/// option wins.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_PATTERN_CONSTRAINT
"adbc.metadata.filter_pattern.constraint"
+
+/// \brief Filter the collection on the constraint types.
+///
+/// Separator: comma (',').
+/// The type is char*.
+#define ADBC_METADATA_FILTER_CONSTRAINT_TYPES
"adbc.metadata.filter.constraint_types"
+
+/// \brief Filter the collection on the literal routine name.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_ROUTINE "adbc.metadata.filter.routine"
+
+/// \brief Filter the collection on the routine name, matching a search
+/// pattern.
+///
+/// If both this and ADBC_METADATA_FILTER_ROUTINE are set, then the last set
+/// option wins.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_PATTERN_ROUTINE
"adbc.metadata.filter_pattern.routine"
+
+/// \brief Filter the collection on the routine types.
+///
+/// Separator: comma (',').
+/// The type is char*.
+#define ADBC_METADATA_FILTER_ROUTINE_TYPES "adbc.metadata.filter.routine_types"
+
+/// \brief Get or set a pagination token.
+///
+/// Some drivers may support this to allow fetching a large metadata
+/// collection in multiple calls. If the pagination token could not be used,
+/// the driver should return an error.
+#define ADBC_METADATA_OPTION_PAGINATION_TOKEN "adbc.metadata.pagination_token"
+
+/// \brief The "meta" collection returns the available metadata collections.
+///
+/// | Field Name | Field Type | Comments |
+/// |--------------------------|------------------------------|----------|
+/// | collection_name | utf8 not null | (1) |
+/// | collection_description | utf8 | (2) |
+/// | collection_schema | extension<arrow.schema_json> | |
+/// | collection_filters | list<FILTER_SCHEMA> | |
+///
+/// (1) The name used to retrieve the collection.
+/// (2) A description of the collection's contents. Not required for
+/// collections defined in this header.
+///
+/// FILTER_SCHEMA is a Struct with fields:
+///
+/// | Field Name | Field Type | Comments |
+/// |--------------------------|------------------------------|----------|
+/// | filter_name | utf8 not null | (1) |
+/// | filter_type | int8 not null | (2) |
+/// | required | bool not null | |
+/// | filter_documentation | utf8 | |
+///
+/// (1) The option key used to set the filter.
+/// (2) A bitfield of ADBC_OPTION_TYPE values.
+#define ADBC_METADATA_COLLECTION_META "meta"
+
+/// \brief The "catalogs" collection returns the catalogs defined in the
+/// database.
+///
+/// Some systems may not have the concept of catalogs, in which case it is
+/// recommended that this collection should contain no rows.
+///
+/// | Field Name | Field Type | Comments |
+/// |--------------------------|------------------------------|----------|
+/// | catalog_name | utf8 | |
+/// | catalog_remarks | utf8 | (1) |
+///
+/// (1) A description of the catalog.
+///
+/// Supported filters:
+/// - ADBC_METADATA_FILTER_CATALOG
+/// - ADBC_METADATA_FILTER_PATTERN_CATALOG
+#define ADBC_METADATA_COLLECTION_CATALOGS "catalogs"
+
+/// \brief The "schemas" collection returns the schemas defined in the
+/// database.
+///
+/// Some systems may not have the concept of catalogs or schemas. If
+/// catalogs are not supported, it is recommended to set catalog_name to
+/// NULL. If schemas are not supported, it is recommended that this
+/// collection should contain no rows.
+///
+/// | Field Name | Field Type | Comments |
+/// |--------------------------|------------------------------|----------|
+/// | catalog_name | utf8 | |
+/// | db_schema_name | utf8 not null | |
+/// | db_schema_remarks | utf8 | (1) |
+///
+/// (1) A description of the schema.
+///
+/// Supported filters:
+/// - ADBC_METADATA_FILTER_CATALOG
+/// - ADBC_METADATA_FILTER_PATTERN_CATALOG
+/// - ADBC_METADATA_FILTER_DB_SCHEMA
+/// - ADBC_METADATA_FILTER_PATTERN_DB_SCHEMA
+#define ADBC_METADATA_COLLECTION_SCHEMAS "schemas"
+
+/// \brief The "tables" collection returns the tables defined in the
+/// database.
+///
+/// | Field Name | Field Type | Comments |
+/// |--------------------------|------------------------------|----------|
+/// | catalog_name | utf8 | |
+/// | db_schema_name | utf8 | |
+/// | table_name | utf8 not null | |
+/// | table_type | utf8 not null | |
+/// | table_definition | utf8 | (1) |
+/// | table_remarks | utf8 | (2) |
+/// | table_schema | extension<arrow.schema_json> | (3) |
+///
+/// (1) The table or view definition (e.g. the SQL DDL statement).
+/// (2) A description of the table.
+/// (3) The Arrow schema of the table, equivalent to
+/// AdbcConnectionGetTableSchema.
+///
+///
+/// Supported filters:
+/// - ADBC_METADATA_FILTER_CATALOG
+/// - ADBC_METADATA_FILTER_PATTERN_CATALOG
+/// - ADBC_METADATA_FILTER_DB_SCHEMA
+/// - ADBC_METADATA_FILTER_PATTERN_DB_SCHEMA
+/// - ADBC_METADATA_FILTER_TABLE
+/// - ADBC_METADATA_FILTER_PATTERN_TABLE
+/// - ADBC_METADATA_FILTER_TABLE_TYPES
+#define ADBC_METADATA_COLLECTION_TABLES "tables"
+
+/// \brief The "columns" collection returns table columns.
+///
+/// | Field Name | Field Type | Comments |
+/// |--------------------------|------------------------------|----------|
+/// | catalog_name | utf8 | |
+/// | db_schema_name | utf8 | |
+/// | table_name | utf8 not null | |
+/// | column_name | utf8 not null | |
+/// | ordinal_position | int32 | (1) |
+/// | remarks | utf8 | (2) |
+/// | xdbc_data_type | int16 | (3) |
+/// | xdbc_type_name | utf8 | (3) |
+/// | xdbc_column_size | int32 | (3) |
+/// | xdbc_decimal_digits | int16 | (3) |
+/// | xdbc_num_prec_radix | int16 | (3) |
+/// | xdbc_nullable | int16 | (3) |
+/// | xdbc_column_def | utf8 | (3) |
+/// | xdbc_sql_data_type | int16 | (3) |
+/// | xdbc_datetime_sub | int16 | (3) |
+/// | xdbc_char_octet_length | int32 | (3) |
+/// | xdbc_is_nullable | utf8 | (3) |
+/// | xdbc_scope_catalog | utf8 | (3) |
+/// | xdbc_scope_schema | utf8 | (3) |
+/// | xdbc_scope_table | utf8 | (3) |
+/// | xdbc_is_autoincrement | bool | (3) |
+/// | xdbc_is_generatedcolumn | bool | (3) |
+/// | xdbc_source_data_type | bool | (3) |
+///
+/// 1. The column's ordinal position in the table (starting from 1).
+/// 2. Database-specific description of the column.
+/// 3. Optional value. Should be null if not supported by the driver.
+/// xdbc_ values are meant to provide JDBC/ODBC-compatible metadata
+/// in an agnostic manner.
+///
+/// Supported filters:
+/// - ADBC_METADATA_FILTER_CATALOG
+/// - ADBC_METADATA_FILTER_PATTERN_CATALOG
+/// - ADBC_METADATA_FILTER_DB_SCHEMA
+/// - ADBC_METADATA_FILTER_PATTERN_DB_SCHEMA
+/// - ADBC_METADATA_FILTER_TABLE
+/// - ADBC_METADATA_FILTER_PATTERN_TABLE
+/// - ADBC_METADATA_FILTER_TABLE_TYPES
+/// - ADBC_METADATA_FILTER_COLUMN
+/// - ADBC_METADATA_FILTER_PATTERN_COLUMN
+#define ADBC_METADATA_COLLECTION_COLUMNS "columns"
+
+/// \brief The "imported_keys" collection, given a table, describes the
+/// primary key(s) referenced by the given table's foreign key(s).
+///
+/// | Field Name | Field Type | Comments |
+/// |--------------------------|-------------------------|----------|
+/// | pk_catalog_name | utf8 | |
+/// | pk_schema_name | utf8 | |
+/// | pk_table_name | utf8 not null | |
+/// | pk_column_name | utf8 not null | |
+/// | pk_name | utf8 | |
+/// | fk_catalog_name | utf8 | |
+/// | fk_schema_name | utf8 | |
+/// | fk_table_name | utf8 not null | |
+/// | fk_column_name | utf8 not null | |
+/// | fk_name | utf8 | |
+/// | key_seq | int16 | (1) |
+/// | constraint_update_rule | int16 | (2) |
+/// | constraint_delete_rule | int16 | (3) |
+/// | constraint_enforced | bool | (3) |
+/// | constraint_deferrability | int16 | (4) |
+/// | constraint_match_type | int16 | (5) |
+///
+/// 1. The 1-based index of the column pair within the foreign key (1 => first
+/// column of the foreign key, 2 => second column of the foreign key, ...).
+/// 2. If applicable, the action to be taken when the primary key is updated
+/// or deleted. The value is one of the ADBC_CONSTRAINT_ACTION_ constants.
+/// 3. Whether the constraint is currently enabled.
+/// 4. Whether the constraint can be deferred, and if so, whether it starts
+/// deferred. The value is one of the ADBC_CONSTRAINT_DEFERRABLE_
+/// constants or ADBC_CONSTRAINT_NOT_DEFERRABLE.
+/// 5. How the foreign key constraint should be matched. The value is one of
+/// the ADBC_CONSTRAINT_MATCH_ constants.
+///
+/// Supported filters:
+/// - ADBC_METADATA_FILTER_CATALOG (applies to fk_catalog_name)
+/// - ADBC_METADATA_FILTER_DB_SCHEMA (applies to fk_schema_name)
+/// - ADBC_METADATA_FILTER_TABLE (required; applies to fk_table_name)
+#define ADBC_METADATA_COLLECTION_IMPORTED_KEYS "imported_keys"
+
+/// \brief The "exported_keys" collection, given a table, describes the
+/// foreign key(s) referencing the given table's primary key(s).
+///
+/// | Field Name | Field Type | Comments |
+/// |--------------------------|-------------------------|----------|
+/// | pk_catalog_name | utf8 | |
+/// | pk_schema_name | utf8 | |
+/// | pk_table_name | utf8 not null | |
+/// | pk_column_name | utf8 not null | |
+/// | pk_name | utf8 | |
+/// | fk_catalog_name | utf8 | |
+/// | fk_schema_name | utf8 | |
+/// | fk_table_name | utf8 not null | |
+/// | fk_column_name | utf8 not null | |
+/// | fk_name | utf8 | |
+/// | key_seq | int16 | (1) |
+/// | constraint_update_rule | int16 | (2) |
+/// | constraint_delete_rule | int16 | (3) |
+/// | constraint_enforced | bool | (3) |
+/// | constraint_deferrability | int16 | (4) |
+/// | constraint_match_type | int16 | (5) |
+///
+/// 1. The 1-based index of the column pair within the foreign key (1 => first
Review Comment:
Is there a reason why we're using 1-based indices?
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