\開発者の負担軽減\ 疑似型「internal」を活用したPostgreSQL関数開発の利点
internal型とは?
- 内部処理におけるデータ表現を抽象化し、データベースシステムの柔軟性を高めます。
- 主に、関数の引数や戻り値の型として宣言するために利用されます。
- 列データ型として直接使用することはできません。
internal型の利点
- 開発者のコーディング負担を軽減し、データベースシステムの保守性を向上させます。
- 将来的な内部実装変更を容易にし、データベースの互換性を維持します。
- 内部処理の詳細を隠蔽し、APIをよりシンプルに保ちます。
internal型の注意点
- 関数定義でのみ使用し、内部処理のみに限定する必要があります。
- SQLクエリ内で直接使用しようとすると、エラーが発生します。
- ユーザーによる直接的な操作は想定されていません。
- C language functions: PostgreSQLにC言語で書かれた関数を組み込む機能
- procedural language: SQLを拡張する機能
- trigger: 特定のイベント発生時に自動実行されるデータベース操作を定義する機能
- 具体的な使用方法については、公式ドキュメントや専門書籍を参照することを推奨します。
- データベースシステムの深い理解が必要となるため、上級者向けの機能と言えるでしょう。
- internal型は、PostgreSQL内部処理を抽象化し、柔軟性と保守性を向上させるための高度な機能です。
Trigger Function with internal trigger data type
CREATE OR REPLACE FUNCTION my_trigger_function()
RETURNS trigger AS $$
DECLARE
old_value record;
BEGIN
-- Access the old row value using the internal trigger data type
old_value := NEW;
-- Perform some operation on the old row value
UPDATE my_table
SET updated_column = old_value.column_name + 1
WHERE id = old_value.id;
-- Return the trigger result (no modification required)
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
Procedural Language Function with internal language handler data type
CREATE OR REPLACE FUNCTION my_plpgsql_function()
RETURNS language_handler AS $$
DECLARE
handler record;
BEGIN
-- Create a language handler using the internal language handler data type
handler := plpgsql_create_language_handler();
-- Perform some operation using the language handler
plpgsql_exec(handler, 'SELECT * FROM my_table;');
-- Return the language handler
RETURN handler;
END;
$$ LANGUAGE plpgsql;
C Language Function with internal fdw_handler data type
CREATE OR REPLACE FUNCTION my_c_function()
RETURNS fdw_handler AS '
#include <postgres/fdw.h>
PG_FUNCTION_DEF(my_c_function)
{
FdwHandler *handler;
handler = (FdwHandler *) palloc(sizeof(FdwHandler));
/* Initialize the FdwHandler structure */
handler->startup = my_fdw_startup;
handler->get_fmgr = my_fdw_get_fmgr;
handler->get_validator = my_fdw_get_validator;
handler->scan = my_fdw_scan;
handler->execute = my_fdw_execute;
handler->close = my_fdw_close;
return handler;
}
';
- It's crucial to note that internal data types are not intended for direct user interaction and should only be used within function definitions.
- The internal data types are used to represent specific data structures or functionality related to the function's purpose.
- These examples demonstrate the usage of internal data types within function definitions.
- A thorough understanding of PostgreSQL internals and function development is essential for working with internal data types effectively.
- These examples are for illustrative purposes only and may require additional context or adjustments for specific use cases.
Opaque Data Types
- They can be used to represent complex data structures or encapsulate internal function logic while maintaining a clean interface.
- Opaque data types, introduced in PostgreSQL 10, provide a way to define custom data structures without exposing their internal implementation details to users.
Example
CREATE TYPE my_opaque_type AS OPAQUE;
Domain Specific Types (DSTs)
- They are particularly useful for representing domain-specific concepts or ensuring data integrity within applications.
- DSTs allow for the creation of user-defined data types that enforce specific constraints and behaviors.
Example
CREATE DOMAIN money AS numeric(10,2) NOT NULL CHECK (value >= 0);
Abstract Data Types (ADTs)
- They involve defining custom functions and operators for manipulating the abstract data type.
- ADTs provide a more comprehensive approach to data type abstraction, encompassing both the data representation and associated operations.
Example
CREATE TYPE point AS (x real, y real);
CREATE FUNCTION point_add(p1 point, p2 point)
RETURNS point AS $$
SELECT x + p2.x, y + p2.y
FROM point p1, point p2;
$$ LANGUAGE sql;
Temporary Tables
- They provide a way to manage temporary data without cluttering the main database schema.
- Temporary tables can be used to store intermediate results or data structures within a function's execution context.
Example
CREATE TEMPORARY TABLE temp_data (
column1 data_type,
column2 data_type
);
INSERT INTO temp_data VALUES (value1, value2);
-- Process data stored in the temporary table
External Libraries
- This approach allows leveraging existing code and expertise while maintaining separation of concerns.
- For complex data processing or specialized functionality, integrating external libraries or tools can be an effective solution.
Example
- Utilizing a C library for image processing tasks within a PostgreSQL function.
The choice between these alternatives depends on various factors, including the complexity of the data structure, the need for data validation or operations, and the desired level of abstraction.
External Expertise
For specialized tasks beyond PostgreSQL's core capabilities, external libraries can be integrated.Temporary Data
For managing intermediate results or temporary data structures, temporary tables are a convenient solution.Complex Operations
For data manipulation involving custom functions or operators, ADTs provide a structured approach.Data Integrity
For enforcing data constraints or domain-specific rules, DSTs or ADTs offer more control.Encapsulation
If the goal is to hide internal implementation details, opaque types or DSTs can be suitable choices.