lidavidm commented on issue #60:
URL: https://github.com/apache/arrow-adbc/issues/60#issuecomment-1211134073
How about this? The parameters are always encoded as a schema, but unknown
types are represented as just NullType. Avoids having lots of optional
things/multiple calls.
```diff
diff --git a/adbc.h b/adbc.h
index e7d9d51..2748d0d 100644
--- a/adbc.h
+++ b/adbc.h
@@ -746,6 +746,22 @@ AdbcStatusCode AdbcStatementBindStream(struct
AdbcStatement* statement,
struct ArrowArrayStream* values,
struct AdbcError* error);
+/// \brief Get the schema for bound parameters.
+///
+/// This should be called after AdbcStatementPrepare. This retrieves
+/// an Arrow schema describing the number, names, and types of the
+/// parameters in a parameterized statement. Not all drivers will
+/// support this. If the name of a parameter cannot be determined,
+/// the name of the corresponding field in the schema will be an empty
+/// string. Similarly, if the type cannot be statically determined,
+/// the type of the corresponding field will be NA (NullType).
+///
+/// \return ADBC_STATUS_NOT_IMPLEMENTED if the schema cannot be determined.
+ADBC_EXPORT
+AdbcStatusCode AdbcStatementGetParameterSchema(struct AdbcStatement*
statement,
+ struct ArrowSchema* schema,
+ struct AdbcError* error);
+
/// \brief Read the result of a statement.
///
/// This method can be called only once per execution of the
diff --git
a/java/core/src/main/java/org/apache/arrow/adbc/core/AdbcStatement.java
b/java/core/src/main/java/org/apache/arrow/adbc/core/AdbcStatement.java
index b621587..fbc1d5f 100644
--- a/java/core/src/main/java/org/apache/arrow/adbc/core/AdbcStatement.java
+++ b/java/core/src/main/java/org/apache/arrow/adbc/core/AdbcStatement.java
@@ -22,6 +22,7 @@ import java.util.Collections;
import java.util.List;
import org.apache.arrow.vector.VectorSchemaRoot;
import org.apache.arrow.vector.ipc.ArrowReader;
+import org.apache.arrow.vector.types.pojo.Schema;
public interface AdbcStatement extends AutoCloseable {
/** Set a generic query option. */
@@ -75,6 +76,20 @@ public interface AdbcStatement extends AutoCloseable {
*/
ArrowReader getArrowReader() throws AdbcException;
+ /**
+ * Get the schema for bound parameters.
+ *
+ * <p>This should be called after AdbcStatementPrepare. This retrieves an
Arrow schema describing
+ * the number, names, and types of the parameters in a parameterized
statement. Not all drivers
+ * will support this. If the name of a parameter cannot be determined,
the name of the
+ * corresponding field in the schema will be an empty string. Similarly,
if the type cannot be
+ * statically determined, the type of the corresponding field will be NA
(NullType).
+ *
+ * @throws AdbcException with {@link AdbcStatusCode#NOT_IMPLEMENTED} if
the parameters cannot be
+ * determined at all.
+ */
+ Schema getParameterSchema() throws AdbcException;
+
/**
* Get a list of partitions of the result set.
*
```
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