many-to-many

问题 I have an existing PostgreSQL database with a many to many relationship, it is handled through a join table as below. I'm looking to apply the ManyToMany Field type, does this bypass this join/intermediate table? How do I correctly configure it in my models.py? I'd rather keep the intermediate table. # models.py class Sample(models.Model): sample_id = models.AutoField(primary_key=True) ... class JoinSampleContainer(models.Model): id = models.AutoField(primary_key=True) container_id = models

问题 I am creating a schema where the following logic applies: A String can belong to multiple locations. Multiple Locations can have multiple String , or no String . The DateTime (As DateScraped ) at which the relationship between Location and String was formed must be recorded. Basically, I've mapped the relationship as a many-to-many relationship using a junction table like so: In mapping the chart in Code First EF6 (Using SQLite), I have the following objects: public class Location { [Key,

问题 I am creating a schema where the following logic applies: A String can belong to multiple locations. Multiple Locations can have multiple String , or no String . The DateTime (As DateScraped ) at which the relationship between Location and String was formed must be recorded. Basically, I've mapped the relationship as a many-to-many relationship using a junction table like so: In mapping the chart in Code First EF6 (Using SQLite), I have the following objects: public class Location { [Key,

问题 I am creating a schema where the following logic applies: A String can belong to multiple locations. Multiple Locations can have multiple String , or no String . The DateTime (As DateScraped ) at which the relationship between Location and String was formed must be recorded. Basically, I've mapped the relationship as a many-to-many relationship using a junction table like so: In mapping the chart in Code First EF6 (Using SQLite), I have the following objects: public class Location { [Key,

问题 I have a table Users and a table Friends which maps users to other users as each user can have many friends. This relation is obviously symmetric: if user A is a friend of user B then user B is also a friend of user A, I only store this relation once. The Friends table has additional fields besides the two User ID's so I have to use an association object. I am trying to define this relationship in declarative style in the Users class (which extends the declarative base), but I can't seem to

问题 I have the following problem with my springboot project: I'm creating a Criteria Query with the elements of a filter, this is the code: public List<IncidentMinimalPOJO> getPOJOFiltered(FilterPOJO filterValue) { List<IncidentMinimalPOJO> resultListPOJO = null; CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Incident> cq = cb.createQuery(Incident.class); List<Predicate> predicates = new ArrayList<>(); Root<Incident> root = cq.from(Incident.class); if (filterValue.getInfodesk() !=

问题 I have the following models: class ProductColor(models.Model): color_title = models.CharField(max_length=50) class BasicProduct(models.Model): product_title = models.CharField(max_length=150) product_desc = models.TextField() product_price = models.FloatField(default=10.0) # Describes what colors are available for this product product_colors = models.ManyToManyField(ProductColor) class BasicCartItem(models.Model): cart_product = models.ForeignKey(BasicProduct) cart_color = models.ForeignKey

问题 I am trying to order products by thp price in options table the price can be in multi currency for that i add dolor_price calculated as code below. but the result was the following Error SQLSTATE[42S22]: Column not found: 1054 Unknown column 'options.dolor_price' in 'order clause' $products=Product::with(["options"=> function($option){ $option->where('name' ,'unique name' ); $option->selectSub(function ($q) { $rateEruToDolor =2; $rateAedToDolor =3; $q->selectRaw(' IF(currency=0,price * ?, IF

问题 I'm have this Many To Many Relationship: public class Role { [Key] public int role_Id { get; set; } public string Name { get; set; } public ICollection<LoginModel> Users { get; set; } public ICollection<Permission> Permissions { get; set; } public Role() { Users = new List<LoginModel>(); Permissions = new Collection<Permission>(); } } public class Permission { [Key] public int permi_Id { get; set; } public string Name { get; set; } public virtual ICollection<Role> Roles { get; set; } public

问题 This question already has an answer here : Entity Framework Core many-to-many navigation issues (1 answer) Closed 10 months ago . as you know we don't have automatic Many to Many Relations between Entities in EF Core. whats the best solution to achieve that? here what I create for do that: class Student { public int StudentId { get; set; } public string Name { get; set; } public string Family { get; set; } public List<StudentCourse> Courses { get; set; } } class Course { public int CourseId {