クエリのフィールドをモデルのフィールドにマップする¶

raw() は自動的にクエリのフィールドをモデルのフィールドにマップします。

The order of fields in your query doesn’t matter. In other words, both of the following queries work identically:

>>> Person.objects.raw("SELECT id, first_name, last_name, birth_date FROM myapp_person")
>>> Person.objects.raw("SELECT last_name, birth_date, first_name, id FROM myapp_person")

Matching is done by name. This means that you can use SQL’s AS clauses to map fields in the query to model fields. So if you had some other table that had Person data in it, you could easily map it into Person instances:

>>> Person.objects.raw(
...     """
...     SELECT first AS first_name,
...            last AS last_name,
...            bd AS birth_date,
...            pk AS id,
...     FROM some_other_table
...     """
... )

名称が一致している限り、そのモデルのインスタンスは適切に生成されます。

Alternatively, you can map fields in the query to model fields using the translations argument to raw(). This is a dictionary mapping names of fields in the query to names of fields on the model. For example, the above query could also be written:

>>> name_map = {"first": "first_name", "last": "last_name", "bd": "birth_date", "pk": "id"}
>>> Person.objects.raw("SELECT * FROM some_other_table", translations=name_map)

インデックスの利用¶

raw() supports indexing, so if you need only the first result you can write:

>>> first_person = Person.objects.raw("SELECT * FROM myapp_person")[0]

However, the indexing and slicing are not performed at the database level. If you have a large number of Person objects in your database, it is more efficient to limit the query at the SQL level:

>>> first_person = Person.objects.raw("SELECT * FROM myapp_person LIMIT 1")[0]

モデルのフィールドの遅延評価¶

Fields may also be left out:

>>> people = Person.objects.raw("SELECT id, first_name FROM myapp_person")

The Person objects returned by this query will be deferred model instances (see defer()). This means that the fields that are omitted from the query will be loaded on demand. For example:

>>> for p in Person.objects.raw("SELECT id, first_name FROM myapp_person"):
...     print(
...         p.first_name,  # This will be retrieved by the original query
...         p.last_name,  # This will be retrieved on demand
...     )
...
John Smith
Jane Jones

From outward appearances, this looks like the query has retrieved both the first name and last name. However, this example actually issued 3 queries. Only the first names were retrieved by the raw() query — the last names were both retrieved on demand when they were printed.

There is only one field that you can’t leave out – the primary key field. Django uses the primary key to identify model instances, so it must always be included in a raw query. A FieldDoesNotExist exception will be raised if you forget to include the primary key.

付加情報の追加¶

You can also execute queries containing fields that aren’t defined on the model. For example, we could use PostgreSQL’s age() function to get a list of people with their ages calculated by the database:

>>> people = Person.objects.raw("SELECT *, age(birth_date) AS age FROM myapp_person")
>>> for p in people:
...     print("%s is %s." % (p.first_name, p.age))
...
John is 37.
Jane is 42.
...

You can often avoid using raw SQL to compute annotations by instead using a Func() expression.

raw() にパラメータを渡す¶

If you need to perform parameterized queries, you can use the params argument to raw():

>>> lname = "Doe"
>>> Person.objects.raw("SELECT * FROM myapp_person WHERE last_name = %s", [lname])

params is a list or dictionary of parameters. You’ll use %s placeholders in the query string for a list, or %(key)s placeholders for a dictionary (where key is replaced by a dictionary key), regardless of your database engine. Such placeholders will be replaced with parameters from the params argument.

>>> query = "SELECT * FROM myapp_person WHERE last_name = %s" % lname
>>> Person.objects.raw(query)

>>> query = "SELECT * FROM myapp_person WHERE last_name = '%s'"

データベース接続とカーソル¶

connection と cursor の実装は PEP 249 に規定された Python DB-API の基準にほぼ完全に準拠しています — トランザクション操作 は例外となります。

Python DB-API に精通していない場合、cursor.execute() 内の SQL 文には直接値を追加せずに、"%s" というプレースホルダーを利用する事に注意してください。この手法を用いる事で、内部で動作しているデータベースライブラリは自動的に必要に応じて値のエスケープを行ってくれます。

加えて Django はプレースホルダーとして Python に内蔵された SQLite モジュールで用いられる "?" でなく "%s" を期待して動作する事にも注意してください。これは全体の調和と健全性のためです。

コンテキストマネージャとしてのカーソルの利用:

with connection.cursor() as c:
    c.execute(...)

これは以下と同じです:

c = connection.cursor()
try:
    c.execute(...)
finally:
    c.close()