Múltiplos M2M em Django

Question

Eu tenho dois modelos no Django para um jogo baseado em mapas 2D:

class Block(models.Model):
   type = models.IntegerField()

class ShopBuilding(models.Model):
   house_blocks = models.ManyToManyField(Block)
   street_blocks = models.ManyToManyField(Block)
   river_blocks = models.ManyToManyField(Block)
   decoration_blocks = models.ManyToManyField(Block)
   npc_blocks = models.ManyToManyField(Block)

Agora só quero associar esses dois modelos usando UMA tabela:

class ShopBlockAssoc(models.Model):
    block = models.ForeignKey(Block)
    shop = models.foreignKey(Shop)

Depois de definir o through campo em ShopBuilding modelo, Django gerou múltiplas falhas quando sincronizado, como

    Error: One or more models did not validate:
tnew.shopbuilding: Accessor for m2m field 'house_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'house_blocks'.
tnew.shopbuilding: Accessor for m2m field 'house_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'house_blocks'.
tnew.shopbuilding: Accessor for m2m field 'house_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'house_blocks'.
tnew.shopbuilding: Accessor for m2m field 'house_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'house_blocks'.
tnew.shopbuilding: Accessor for m2m field 'street_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'street_blocks'.
tnew.shopbuilding: Accessor for m2m field 'street_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'street_blocks'.
tnew.shopbuilding: Accessor for m2m field 'street_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'street_blocks'.
tnew.shopbuilding: Accessor for m2m field 'street_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'street_blocks'.
tnew.shopbuilding: Accessor for m2m field 'river_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'river_blocks'.
tnew.shopbuilding: Accessor for m2m field 'river_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'river_blocks'.
tnew.shopbuilding: Accessor for m2m field 'river_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'river_blocks'.
tnew.shopbuilding: Accessor for m2m field 'river_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'river_blocks'.
tnew.shopbuilding: Accessor for m2m field 'decoration_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'decoration_blocks'.
tnew.shopbuilding: Accessor for m2m field 'decoration_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'decoration_blocks'.
tnew.shopbuilding: Accessor for m2m field 'decoration_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'decoration_blocks'.
tnew.shopbuilding: Accessor for m2m field 'decoration_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'decoration_blocks'.
tnew.shopbuilding: Accessor for m2m field 'npc_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'npc_blocks'.
tnew.shopbuilding: Accessor for m2m field 'npc_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'npc_blocks'.
tnew.shopbuilding: Accessor for m2m field 'npc_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'npc_blocks'.
tnew.shopbuilding: Accessor for m2m field 'npc_blocks' clashes with related m2m field 'Block.shopbuilding_set'. Add a related_name argument to the definition for 'npc_blocks'.

Se eu definir db_table campo Django diz:

The model has two manually-defined m2m relations through the model, which is not permitted. Please consider using an extra field on your intermediary model instead.

Como eu poderia consertar isso?Eu realmente quero ter certeza de que essas relações shop-block estão usando o mesmo modelo associado intermediário com o mesmo db_table

Answer 1

O problema é que no modelo Block ele tenta criar links para trás.Django nomeia esses links com base no Model, no seu caso para todos os ManyToMany que ele tenta criar shopbuilding_set e nomes colidem.Para evitar isso adicione related_name, por exemplo:

class ShopBuilding(models.Model):
   house_blocks = models.ManyToManyField(Block, related_name="shopbuilding_house_set")
   street_blocks = models.ManyToManyField(Block, related_name="shopbuilding_street_set")
   river_blocks = models.ManyToManyField(Block, related_name="shopbuilding_river_set")
   decoration_blocks = models.ManyToManyField(Block, related_name="shopbuilding_decoration_set")
   npc_blocks = models.ManyToManyField(Block, related_name="shopbuilding_npc_set")

Então você poderá acessar ShopBuilding de Block instância como esta:

block.shopbuilding_npc_set.all()