带有额外字段的Django ManyToMany字段在两种关系中均不显示 [英] Django ManyToMany field through with extra fields does not show on both relations

问题描述

我有一堂课 Assembly

class Assembly(models.Model):

    room = models.ForeignKey("Room", related_name="assemblies")
    name = models.CharField(max_length=200)
    number = models.IntegerField()
    position = models.CharField(max_length=200, blank=True)
    components = models.ManyToManyField("material.Component", through="m2m_Assembly_Components")
    connections = models.ManyToManyField("Assembly", through="Connection")
    category = models.ForeignKey("Category", default=0)
    notes = models.TextField(blank=True)

在其实例(连接)之间具有ManyToMany Realtionship.我使用中间表 Connection ，这样我可以在 Assembly 的两个实例之间建立用于连接的其他字段.

that has a ManyToMany Realtionship between instances of itself (connections). I use an intermediary table Connection so that i can have additional fields for a connection between two instances of an Assembly.

class Connection(models.Model):

    source = models.ForeignKey("Assembly", related_name="source_assembly", null=True)
    destination = models.ForeignKey("Assembly", related_name="destination_assembly", null=True)
    length = models.IntegerField(null=True, blank=True)

如果我有两个程序集，比如说A和B，然后通过定义一个新的Connection(使用A作为源，B作为目标)来连接它们，我将B作为A的连接( A.connections.all())，但我没有得到A作为B的连接.

If I have two Assemblies, lets say A and B, and I connect them by defining a new Connection with A as source and B as destination, I get B as A's connections (A.connections.all()), but I don't get A as B's connections.

如果我不使用中间表，只需一个 models.ManyToManyField("Assembly")我将A作为B的连接并将B作为A的连接.

If I don't use an intermediary table, just a models.ManyToManyField("Assembly") I get A as B's connections and B as A's connections.

我这是什么问题?

推荐答案

关注有关

使用中间模型的递归关系始终定义为非对称的-即，使用 symmetrical = False –因此，存在源" 的概念和目标" .在这种情况下，'field1'将被视为关系的"source" ，而'field2'将被视为关系的"target".

Recursive relationships using an intermediary model are always defined as non-symmetrical – that is, with symmetrical=False – therefore, there is the concept of a "source" and a "target". In that case 'field1' will be treated as the "source" of the relationship and 'field2' as the "target".

，在您的情况下，它是 source 和 destination .

and, in your case it is source and destination.

由于您正在使用中介模型 Connection ，因此该关系不再对称.因此， A.connections.all()和 B.connections.all()将返回不同的结果.

Since you are using an intermediary model Connection, the relationship is not symmetrical anymore. Therefore, A.connections.all() and B.connections.all() will return different results.

A.connections.all() #all assemblies where A is source
B.connections.all() # all assemblies where B is source

如果添加连接:

Connection(source=A, destination=B)

您可以使用以下命令找到所有以B为目标的程序集:

you can find all the assemblies where B is destination using:

B.destination_assembly.all().values_list('source', flat=True) # this will include A

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