many-to-many

问题 I have many-to-many relation with three tables: Category , Product , ProductCategory . Relation in Category : public function getProductCategories() { return $this->hasMany(ProductCategory::className(), ['category_id' => 'id']); } Relation in Product : public function getProductCategories() { return $this->hasMany(ProductCategory::ClassName(), ['product_id' => 'id']); } And in ProductCategory public function getProduct() { return $this->hasOne(Product::className(), ['id' => 'product_id']); }

问题 I have a many-to-many relationship in my MySQL-database with three tables like this: TABLE item, TABLE relation (storing only ids of items and tags), TABLE tag Each item can have multiple tags also tags can be related to multiple items, e.g. the item "shoe" can have the tags "sport" and "leather" while the tag "sport" could be related to items "shoe" and "shirt". What I need to do now is select all items that have one or many tags combined by an AND-condition, so e.g. I'd like to find all

问题 Below is my database structure in firebase . I only have signed-in users Id. User -userId -Name -age -groups groupId1:true groupId2:true Group -groupId -name -desc -UserId -UserId1:true -UserId2:true I want to list the details of all the groups that user belongs to. My approach is, Find all the groups my user belongs to by checking the index from User. Using the list of groupid we got from step1, get details of group from Groups. Is there any other better suggestions? 回答1: With your current

问题 I have two models: AffectedSegment model class AffectedSegment(models.Model): SEGMENTO_ESCAPULA = 'Escápula' SEGMENTO_HOMBRO = 'Hombro' SEGMENTO_CODO = 'Codo' SEGMENTO_ANTEBRAZO = 'Antebrazo' SEGMENTO_CARPO_MUNECA = 'Carpo/Muñeca' SEGMENTO_MANO = 'Mano' SEGMENT_CHOICES = ( (SEGMENTO_ESCAPULA, u'Escápula'), (SEGMENTO_HOMBRO, u'Hombro'), (SEGMENTO_CODO, u'Codo'), (SEGMENTO_ANTEBRAZO, u'Antebrazo'), (SEGMENTO_CARPO_MUNECA, u'Carpo/Muñeca'), (SEGMENTO_MANO, u'Mano'), ) affected_segment = models

问题 I have two models: AffectedSegment model class AffectedSegment(models.Model): SEGMENTO_ESCAPULA = 'Escápula' SEGMENTO_HOMBRO = 'Hombro' SEGMENTO_CODO = 'Codo' SEGMENTO_ANTEBRAZO = 'Antebrazo' SEGMENTO_CARPO_MUNECA = 'Carpo/Muñeca' SEGMENTO_MANO = 'Mano' SEGMENT_CHOICES = ( (SEGMENTO_ESCAPULA, u'Escápula'), (SEGMENTO_HOMBRO, u'Hombro'), (SEGMENTO_CODO, u'Codo'), (SEGMENTO_ANTEBRAZO, u'Antebrazo'), (SEGMENTO_CARPO_MUNECA, u'Carpo/Muñeca'), (SEGMENTO_MANO, u'Mano'), ) affected_segment = models

问题 I'm having trouble with a SQL query. My schema describes a many to many relationship between articles in the articles table and categories in the categories table - with the intermediate table article_category which has an id , article_id and category_id field. I want to select all articles which only have the categories with id 1 and 2 . Unfortunately this query will also select any articles which have those categories in addition to any others. For example, this is a sample output from the

问题 I have a basic understanding of SQL databases and I might overlooked something, but I cannot figure out the following problem: there is a many-to-many relationship (for example: users - user_roles - roles). Is it possible to add (new) role to a (new) user with one SQL command (atomic operation)? Currently I use Sqlite. I am aware of the SELECT last_insert_rowid(); command and with this and several SQL commands I can achieve what I want. But I want to incorporate it into one command (so the

问题 I have a basic understanding of SQL databases and I might overlooked something, but I cannot figure out the following problem: there is a many-to-many relationship (for example: users - user_roles - roles). Is it possible to add (new) role to a (new) user with one SQL command (atomic operation)? Currently I use Sqlite. I am aware of the SELECT last_insert_rowid(); command and with this and several SQL commands I can achieve what I want. But I want to incorporate it into one command (so the

问题 I'm developing a mobile application backend with Django 1.9.1 I implemented the follower model and now I want to list all of the followers of a user but I'm currently stuck to do that. I also use Django Rest Framework. This is my UserProfile model class UserProfile(models.Model): # Linking UserProfile to User model. user = models.OneToOneField(User) city = models.CharField(null=True, max_length=30, blank=True) gender = models.CharField(null=True, max_length=10, blank=True) # m for male, f for

问题 I'm developing a mobile application backend with Django 1.9.1 I implemented the follower model and now I want to list all of the followers of a user but I'm currently stuck to do that. I also use Django Rest Framework. This is my UserProfile model class UserProfile(models.Model): # Linking UserProfile to User model. user = models.OneToOneField(User) city = models.CharField(null=True, max_length=30, blank=True) gender = models.CharField(null=True, max_length=10, blank=True) # m for male, f for