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feat(c/driver/postgresql): add arrow.opaque type metadata #2122

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Sep 5, 2024
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feat(c/driver/postgresql): add arrow.opaque type metadata #2122

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20 changes: 20 additions & 0 deletions c/driver/postgresql/postgres_type.h
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Expand Up @@ -312,6 +312,9 @@ class PostgresType {
std::vector<PostgresType> children_;

static constexpr const char* kPostgresTypeKey = "ADBC:postgresql:typname";
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Should the old way of doing this be deprecated now or in some future version?

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Hmm, I guess it can't get a formal deprecation tag but I can update the docs

static constexpr const char* kExtensionName = "ARROW:extension:name";
static constexpr const char* kOpaqueExtensionName = "arrow.opaque";
static constexpr const char* kExtensionMetadata = "ARROW:extension:metadata";

ArrowErrorCode AddPostgresTypeMetadata(ArrowSchema* schema) const {
// the typname_ may not always be set: an instance of this class can be
Expand All @@ -322,8 +325,25 @@ class PostgresType {
nanoarrow::UniqueBuffer buffer;

ArrowMetadataBuilderInit(buffer.get(), nullptr);
// TODO(lidavidm): we have deprecated this in favor of arrow.opaque,
// remove once we feel enough time has passed
NANOARROW_RETURN_NOT_OK(ArrowMetadataBuilderAppend(
buffer.get(), ArrowCharView(kPostgresTypeKey), ArrowCharView(typname)));

// Add the Opaque extension type metadata
std::string metadata = R"({"type_name": ")";
metadata += typname;
metadata += R"(", "vendor_name": "PostgreSQL"})";
NANOARROW_RETURN_NOT_OK(
ArrowMetadataBuilderAppend(buffer.get(), ArrowCharView(kExtensionName),
ArrowCharView(kOpaqueExtensionName)));
NANOARROW_RETURN_NOT_OK(
ArrowMetadataBuilderAppend(buffer.get(), ArrowCharView(kExtensionMetadata),
ArrowStringView{
metadata.c_str(),
static_cast<int64_t>(metadata.size()),
}));

NANOARROW_RETURN_NOT_OK(
ArrowSchemaSetMetadata(schema, reinterpret_cast<char*>(buffer->data)));

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8 changes: 8 additions & 0 deletions c/driver/postgresql/postgres_type_test.cc
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Expand Up @@ -174,6 +174,14 @@ TEST(PostgresTypeTest, PostgresTypeSetSchema) {
&typnameMetadataValue);
EXPECT_EQ(std::string(typnameMetadataValue.data, typnameMetadataValue.size_bytes),
"numeric");
ArrowMetadataGetValue(schema->metadata, ArrowCharView("ARROW:extension:name"),
&typnameMetadataValue);
EXPECT_EQ(std::string(typnameMetadataValue.data, typnameMetadataValue.size_bytes),
"arrow.opaque");
ArrowMetadataGetValue(schema->metadata, ArrowCharView("ARROW:extension:metadata"),
&typnameMetadataValue);
EXPECT_EQ(std::string(typnameMetadataValue.data, typnameMetadataValue.size_bytes),
R"({"type_name": "numeric", "vendor_name": "PostgreSQL"})");
schema.reset();

ArrowSchemaInit(schema.get());
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17 changes: 17 additions & 0 deletions docs/source/driver/postgresql.rst
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Expand Up @@ -329,6 +329,23 @@ being read or written.
overflow/underflow; an error will be returned if this would be
the case.

Unknown Types
~~~~~~~~~~~~~

Types without direct Arrow equivalents can still be returned by the driver.
In this case, the Arrow type will be binary, and the contents will be the raw
bytes as provided by the PostgreSQL wire protocol.

For Arrow implementations that support the :external:doc:`Opaque canonical
extension type <format/CanonicalExtensions>`, the extension type metadata is
also always present. This helps differentiate when the driver intentionally
returned a binary column from when it returned a binary column as a fallback.

.. warning:: Currently, the driver also attaches a metadata key named
``ADBC:posgresql:typname`` to the schema field of the unknown
column, but this has been deprecated in favor of the Opaque type
and you should not rely on this key continuing to exist.

Software Versions
=================

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