I have database with different tables. But I can't get access to some tables, and I'm curious why? For example, there is Projects table and Users table in database, and I need to get list of all users that are in specific Project by Id. These tables have many to many relationship, so there is joining table with ProjectId and UserId. It's logic to use some Join to get users that I need from table Users with help of this joining table from db. But how can I make Join when my DbContext doesn't have joining table? How can I get access to joining table using DbContext, or maybe there are some different ways to get list of users by project id?
If someone have similar problem, here is a simple way to use all the data from collections in model
var project = _db.Projects.Include(x => x.Tickets).ThenInclude(y => y.Users).SingleOrDefault(p => p.Id == id);
so after that you gonna have your model and all the data from collections that you need
ProjectUser - is joining table, use for link two tables. This tables must have (usually) Collection for access to this many-to-many data.
So you can will have collection of users for this project. And doing filtering by users from your Ticket (example from image).
Yes, exists few different ways - setting with ef fluent, or attribute, or dbcontext. Better to find complete guide for many-to-many setting in your application.
Related
I'm on a project with Rails, Postgresql and Active Record, where I have Users, that can be either Influencers, or Creators.
The Users have common columns such as email, password, first_name and last_name, but :
influencers will have followers, eg_rate, account columns
creators will have SIRET_number and specialty columns
How can I design my database so Influencers and Creators are kind of "child" of the Users table ? I mean, is it possible to have a db where I can access a User' followers or a User's specialty with one query, or I'll always have to do multiple queries to achieve this ? I've tried to create three tables for each, with a foreign key user_id in Influencers table and Creators table. I also tried to add a user_type column to my User table where I pass the values of either "influencer" or "creator", but I'm kind of lost on how to link every tables...
Thank you everyone.
Your approach is right.
You can create a table users with the common columns and add a foreign key to influencers and creators tables.
Then when you need to retrieve the data, you can use ActiveRecord relations to easily fetch data and use ActiveRecord's includes method for relations.
For example:
class Creator < ActiveRecord::Base
# The relation must be set
has_one :user
end
# To fetch data anywhere else:
Creator.find_by(SIRET_number: 1234).includes(:user)
If you need to retrieve a creator or influencer by an attribute from related users table, you can use joins:
Creator.joins(:users).where(users: {email: "foo#bar.com"})
Make sure you have the relations set in both User and Creator models.
Check out this topic for more info.
By using includes or joins instead of using creator.user you'll avoiding the unnecessary additional query. The downside is the syntax is now longer, you can maybe create your own getters to easily retrieve data instead of writing "includes" everytime.
Also assuming you're not aware of this method, I suggest you to read about the common N+1 problem with Rails & ActiveRecord. The same methods can solve a lot of problems for you.
I'm trying to create a relation using Fluent API, but I can't get it to work. There are 2 tables: SecurityEntities and SecurityEntityRelations. The SecurityEntities table contains users and groups, the SecurityEntityRelation table is an association table that contains relations between the users and groups (it defines which groups contain which members). I already mamaged to relate the 2 entities within EntityTypeConfiguration:
HasMany(se => se.Groups).WithMany(g => g.Members).Map(seg =>
{
seg.MapLeftKey("ser_EntityName");
seg.MapRightKey("ser_MemberOf");
seg.ToTable("ser_SecurityEntityRelations");
});
This populates the SecurityEntity.Groups and Members properties. But one of the security groups is being concidered a "primary" group, which should be stored in a separate SecurityEntity.PrimaryGroup property. In SQL, this is implemented by a column in the SecurityEntityRelation table, which marks the relation as being "primary". (I know, a self-referencing foreign key in the SecurityEntity table would have been a better solution, but this was designed quite some time ago, and we're stuck with this implementation because our legacy code is also written this way) So, now my question is: how can I create an EF mapping like the one above, which specifies the same relation, but only when column "ser_IsPrimaryGroup" equals a fixed value of '1'?
We have a web portal in our company that is written in asp.net MVC . right now each department have their own database but we want to avoid having multiple database because the database scheme is the same only it has diffrent data inside for each department.like each department has their own projects etc. how the database model should be changed in such a way to avoid having multiple database ?
also we want to share some elments like projects between diffrents department. how it could be done ?
The single database that you have in mind would have to have its table re-designed such that you would be able to tell, for each record in each table, what department the record relates to. Essentially you would need to add a "DeptId" column to each root-level table. By root level table I mean only the parents of foreign key relationships. Eg, if you have an OrderHeader and OrderLines, only the OrderHeader table would need to have this DeptId column. The lines relate to the header, so you won't need to add this column to the lines table as well. Alternatively, if you have a Customer table, such that each customer belongs to only one department, then you would add the DeptId column to this customer table and then you won't need it on the OrderHeader table (since order header should be referencing Customer table)
Those tables/elements that you want to share between databases just would not have the DeptId column added to them.
So I am working on an MVC project to put to work the studying I have been doing. I am wrestling with the concept of Database Table relationships and foreign keys. I am working on a simple ecommerce site (displays products, shopping cart, user accounts..etc).
I have the following tables to start out with:
1) Products
2) Categories
I setup the Products and Categories tables to have a ProductId and CategoryId respectively. In my MySQL db, I created a FK on the Products Table to relate to the CategoryId field on the Categories table (I am not sure this was correct to begin).
My expectations for the way the database would handle the table relationship: I didn't want the DB to do anything with the products table if I deleted a category out of the Categories table, or vise versa. The only thing would be that the category field in a Product would be blank (or default) if their category was removed.
Finally, do I have to do anything in my entity classes such as in the Products class, add the ProductId to the Category.ProductId?
Eventually, when I Orders and Users to the project, I can see a relationship where each user -> many orders -> each order has many products -> and each product is in one category.
But I am having a hard time understanding how or if I should be setting up a Foreign key relationship in the two current tables of Products and Categories and if so how to setup my entity class in relation to that FK.
Any advice.
It has been my experience (with L2S) that you don't want to specify any relationships between tables. I have simply done the PK, FK logic myself. This keeps the L2S generated objects simple and is most likely the way you worked with them before in SQL. That, at least, is the case for me.
I am one of hibernate user in Australia. Recently, I have been dealing with hibernate many-to-many mapping and not going well though.
I got in trouble with "join/associate table with extra columns mapping".
Let`s say there are three tables called Product Order and OrderProduct (includes extra column quantity). Product holds many-to-many relationship with Order.
My confusion is that do we have to consider both ends of associate table when we are writing mapping files? or just write either side?
Also, is it necessary to produce mapping file for the associate table as well?
Any suggestions will be appreciated!!
create a view to join two tables. this view and rest table is many to one relationship
Hope it's userful
You should have an association mapping and entity because you need to create them just like an other entity.