带有连接的 Django ORM SELECT

Question

django 中的模型：

class Key(models.Model):
    id     = models.AutoField(primary_key=True, blank=True)
    name   = models.CharField(max_length=50)


class Record(models.Model):
    id         = models.AutoField(primary_key=True, blank=True)
    project_id = models.IntegerField()
    name       = models.CharField(max_length=50)


class Value(models.Model):
    id        = models.AutoField(primary_key=True, blank=True)
    record    = models.ForeignKey(Record)
    key       = models.ForeignKey(Key)
    value     = models.CharField(max_length=255)

我需要从数据库中选择这些数据：

NAME (from record)
and fields related with this record
[NAME (from key), VALUE (from value)]
[NAME (from key), VALUE (from value)]
[...]

我可以使用 django ORM 进行选择吗？ （例如在 SQL 中选择看起来像这样）

SELECT
    `keeper_record`.`id` AS `record_id`,
    `keeper_record`.`name` AS `name`,
    `keeper_record`.`desc` AS `desc`,
    `keeper_key`.`name` AS `key_name`,
    `keeper_key`.`desc` AS `key_desc`,
    `keeper_value`.`value` AS `value_value`
FROM `keeper_record`
JOIN `keeper_value` ON `keeper_record`.`id` = `keeper_value`.`record_id`
JOIN `keeper_key` ON `keeper_key`.`id` = `keeper_value`.`key_id`
WHERE record_id = id

Answer 1

以下选择与特定记录 id 相关的值。然后您可以按照外键获取相关记录和键。使用select_related 可以最大限度地减少数据库查找。

# Select all values related to a record in your view
record = Record.objects.get(pk=record_id)
values = Value.objects.filter(record=record).select_related()

# In your template
{% for value in values %}
{{ value.record.name }} - {{ value.key.name }} - {{ value.value }}
{% endfor %}

选择多条记录

在您的 sql 中，您有 WHERE record_id = 1，所以我展示了如何获取特定记录的所有值。您还可以在一个查询中选择多个记录的值。

# filter all records which belong to the project with `project_id=1`
records = Record.objects.filter(project_id=1)
# select all values that belong to these records
values = Value.objects.filter(record__in=records).select_related().order_by('record')

Answer 2

应该相对简单，因为您已经将外键绑定在一起。

Record.objects.select_related().filter(id = variable_that_stores_id)

您可以将其与only 结合使用，以限制您想要恢复的字段。