lidavidm commented on code in PR #4694:
URL: https://github.com/apache/arrow-adbc/pull/4694#discussion_r3877126364
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c/include/arrow-adbc/adbc.h:
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@@ -1087,6 +1093,609 @@ 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).
+///
+/// Drivers may add more fields at the end of standard schemas to reflect
+/// vendor-specific metadata. Applications must access these using an offset
+/// from the end of the schema and cannot assume that the index of the field
+/// will remain stable. 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. 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_PATERN_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 catalog 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 Only show namespaces in the given multi-part namespace.
+///
+/// Separator: ASCII unit separator (0x1F).
+/// The type is char*.
+#define ADBC_METADATA_FILTER_NAMESPACE "adbc.metadata.filter.namespace"
+
+/// \brief Only show namespaces with the given name. This filter only applies
+/// to the last namespace component.
+///
+/// The type is char*.
+#define ADBC_METADATA_FILTER_NAMESPACE_NAME
"adbc.metadata.filter.namespace_name"
+
+/// \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 | |
+/// | collection_description | utf8 | |
+/// | collection_schema | extension<arrow.schema_json> | |
Review Comment:
I'm talking to Kent, hopefully we can keep it going. Otherwise, I may
propose an `arrow.schema_ipc` (even if that's a bit ugly)
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