junction-table

I have items and units table that have many to many relationship. In other words, the item has many units and the unit has many items. I managed the relation through a junction table item_units . The junction table has some extra field more than item_id and unit_id , i.e it has price, and weight (it is an integer to manage the order of units for each item for display purposes). I managed the relations in the models as follows: //In Items model /** * @return \yii\db\ActiveQuery */ public function getItemUnits() { return $this->hasMany(ItemUnits::className(), ['item_id' => 'id'])->orderBy(['item

I'm modeling many-to-many relationship where the relationship is accessed most of the time from one side only. It's more like a hierarchy, that is accessed top-down and not the other way around. Survey has and belongs to many Questions has and belongs to many Answers . Both relationships must be many-to-many because a same question can be re-used across different surveys and same answer in many questions. This is a requirement. The standard M2M implementation would use two junction tables, surveys_questions and questions_answers . Instead, I'm thinking about using PostgreSQL's integer arrays

create_table :categories_posts, :id => false do |t| t.column :category_id, :integer, :null => false t.column :post_id, :integer, :null => false end I have a join table (as above) with columns that refer to a corresponding categories table and a posts table. I wanted to enforce a unique constraint on the composite key category_id, post_id in the categories_posts join table. But Rails does not support this (I believe). To avoid the potential for duplicate rows in my data having the same combination of category_id and post_id, what's the best workaround for the absence of a composite key in Rails

I have the following model public class PageConfig : Base { // Properties Etc.. public ICollection<Image> ScrollerImages { get; set; } } My approach is to bind using a junction table { PageConfigID, ImageID }. In my model binder i tried the following.. modelBuilder.Entity<PageConfig>() .HasMany(x => x.ScrollerImages) .WithMany() .Map(x => { x.ToTable("junc_PageConfigScrollerImages"); x.MapLeftKey("PageConfigID"); x.MapRightKey("ImageID"); }); Which results in a null collection of images. How can i bind these Images to the PageConfig model? EDIT Most of the problem was due to user error. jic

I'm trying to create a many-to-many relationship in Entity Framework (code first), according to the following post: Database design for limited number of choices in MVC and Entity Framework? However, I can't get it to work properly, and I'm sure I'm doing something very simple the wrong way. Here's the diagram I have no from my attempts: The point of the junction table is that I need to have an extra property, Level, in the relationship, so I can't just go with a direct relationship between Consultant and Program. I added the ConsultantProgramLink entity manually in the designer, and then