I have next task to do in MySQL:
We have Accounts, Farms, Customers, and Users
An account belongs to a Customer
A User has access to one or more accounts
A User has access to one or more farms tied to that account
A farm is tied to one account
Here is ER Model:
Can someone take a look and check whether I made this correct?
For this SQL modeling task, you have three types of entity relationships: one-to-one, one-to-many and many-to-many (How to implement one-to-one, one-to-many and many-to-many relationships while designing tables? for more detail on their implementation).
In your toy model, if "a User has access to one or more accounts," this is modeled as a one-to-many relationship between the user and the accounts, which requires a foreign id on the many side (i.e. every account has a user_id) but user does not have an account_id.
The account-customer relationship appears to be well-modeled, because it is one-to-one (so either table can hold the foreign key), but your one-to-many relations appear to have some errors.
Related
Consider the scenario between a Project, Task, and a User (ER diagram attached included):
A project can have multiple tasks and a task can be in multiple projects (thus the many-many relationship ProjectTask)
A project can have multiple users and a user can be in multiple projects (thus the many-many relationship ProjectUser)
Check the above example's ER Diagram here
Now a ProjectTask can be assigned to multiple ProjectUsers and a ProjectUser can be assigned multiple ProjectTasks, basically a TasksAssigned relationship
How will I go about storing that information in a database? Can two relationships have a relationship? If yes, is there a better way to showcase this scenario? And if no, how do you show this relationship?
You can have a three-way relationship, in your case:
user
project
task
You probably want to guarantee that the user and task have the same project. That can be handled by declaring composite foreign keys to the projectTasks and projectUsers tables. The structure guarantees that the user and task are in the same project (because it is explicitly mentioned in the row in this table).
I have a simple and probably. banal question. I am working on the first, conceptual phase of an entity-relationship diagram.
This DABMS will be used by some Managers, that will control (registrate and modify accounts) of customers.
In my diagram I have the two entities "MANAGER" and "CUSTOMER". Is it necessary to connect them with a relationship (M:N), to specify that the Managers are those who will manage the customers' account, or this relationship is unnecessary?
to specify that the Managers are those who will manage the customers
No. ER diagrams typically show relations that are reflected in your database.
Example, what would be visible in your ERD
Each customer has a manager assigned who's responsible for this customer => 1:n - each customer has one manager but one manager can be responsible for multible customers.
This question extends the example Eloquent : Working With Pivot Tables provided in the Laravel Documentation.
The relationship here is that a User has many Role objects that it can relate to, and each Role is made up of a number of Task's.
The relationships between these models are:
User and Role:
Each Role may only relate to one User, however a User may have many Role's
A one-to-many relationship
Role and Task
Each Role can have many Task's associated with it, and each Task can belong to several Roles
A many-to-many relationship
In terms of a database schema (MySql), we therefore have:
A users table that has no foreign keys
A roles table with a user_id foreign key
A tasks table
A role-task pivot table
In plain English, the constraint I need to apply is that a user can not be associated with multiple roles that are made up of exactly the same tasks, however two role's can be made up of exactly the same task's
Is there an in-built way to apply this constraint using Laravels Eloquent ORM system? If not, what would be a tidy workaround?
edit:
Eloquent-like description:
User hasMany Role
Role belongsToMany Task
Question: How to prevent assigning to a user multiple roles having exactly the same related collection of tasks
I am designing a product that is mainly to be used by small organizations. The idea is for every member of the organization to have their own accounts (known as subaccounts). At the same time, there needs to be data that can be accessed by anyone with that organization. I am trying to decide between two courses of action.
Separate Table for Organizations
In this design, there would be a organizations table and a users table. The users would be connected to organizations via foreign key, and the shared data would use the foreign id of the organization.
User Conglomerate
Here an additional field in the users table would point to another row in the table (the parent) that represents the primary account for the organization and is linked to all the shared data.
Which approach would be superior in this situation?
Both approaches seem reasonable and workable, but I would lean towards having a separate table for organizations as ultimately the idea of an 'organization' is different to that of an 'user'. You may need to have different attributes for an organization than you would a user (e.g. you may need to have more than one 'superuser' for an organization at some stage), and so having this data in a separate table would make it (a) easier to code against (b) more extensible and future-proof (c) more efficient and normalized in storage.
I want to know in what situations we create many to many relation. What is the need of doing such?
A quick search goes a long way. Though the following is for MS Access, the concept is the same for any relational database.
Via: office.microsoft.com - Create a many-to-many relationship:
You have a many-to-many relationship when a single record in one table
can relate to many records in another, and a single record in that
second table can also relate to many records in the first. For
example, say your company has several types of computers and several
technicians, with each technician certified to work on some, but not
all, of the computers. Each technician can be related to more than one
computer, and in turn, each computer can be related to more than one
technician.
To track who can work on a given machine, you create a many-to-many
relationship by adding the primary keys from both sides of the
relationship to a third table, called a junction or link table. In
other words, a many-to-many relationship is really just a pair of
one-to-many relationships.