I am doing a design of a database, I have built my conceptual entity-relationship model and I have arrived at the physical implementation on mysql workbench. However, I find myself having to manage users who interact with the database.
For example, a student can only view data related to his exams and not all students. To do this I thought of introducing a "login" table containing "username", "password" and "user type" to connect this table to the table that contains the student's data, I should add a "username" attribute to this table .
My question, however, concerns the following question: can I add these tables in the physical schema without inserting appropriate entities in the conceptual E-R schema, or do I have to insert the "login" entity in the conceptual schema as well?
Related
In my database I have
a Members table which contains basic member details (MemberId [primary key - auto generated number], MemberName, IsActive).
a MembersDetails table which contains more detailed information about the member (Address, Phone, Birthday ...). MembersDetails has MemberId field as a foreign key to the Members table.
There's a reason (part of the app logic) that the 2 tables are separated and are not all in one table.
I've created a view that gets a full member details (a join of the 2 tables), and Entity Framework created an object that represents the view.
I have 2 questions:
Is there a better way of flattening 2 joined tables into an object other than creating a view in the database?
I would like to create an object of the view type (a full user details), initialize it's properties and insert it to the database (which will put the info it needs in the Members table, the the generated id, and than insert to the MemberDetails table). Is there a way to do that?
Ad 1.
I think a database view will be a good choice for performance reasons.
But you can investigate an inheritance provided with the Entity Framework.
It allows you join two separated tables in one model object containing all properties (from "derived" and "base" table). Note, it will be OK for one to one relations (but not for one to many).
Implementing Inheritance with the Entity Framework 6 in an ASP.NET MVC 5 Application
Ad 2.
The Entity Framework inheritance will help you with this issue well. Alternatively, if you can use a database view, just create stored procedures for inserting and updating data included in a view, then map the stored procedures for specified actions on the view model generated by Entity Framework.
I have these three tables inside my sql server but when mapping these tables using EF I will lose the table representing the M-M relation -the accountsitemapping table- and in this case I will not be able to know which accounts are linked to which sites.
To workaround this problem I just added a new column to the AccountSiteMapping table and I re-mapped the tables again then I can access the AccountSiteMapping table.
But is there a way to be able to solve this problem without the need to modify my table design ?
By default entity framework will hide all mapping tables in many-to-many relationships. You will have to do your queries this way:
For example, finding SiteDefinitions associated with a given org_ID:
db.SiteDefinitions.Where(a => a.AccountDefinitions.Any(b => b.ORG_ID == org_ID));
I've got a table "Persons" (PersonId, Name, Address) which contains information about people. I then subclass this information with tables "Clients" (PersonId, DateJoined) and Victims (PersonId, DateAssassinated).
In SSMS I have established an FK relationship FK_Clients_Persons and FK_Victims_Persons where the Primary Key is Persons.PersonId and the foreign key is the eponymous field in the Clients and Victims tables respectively. In SSMS I cannot see any obvious functional difference between these relationships.
However, in ADO.NET Entities when I create the model from the database, the tool does not identify FK_Victims_Persons but it does recognise FK_Clients_Persons. It just treats Victims.PersonId as a simple field and doesn't generate relationship members for it. The missing FK relationship does not appear in the Constraints tree of the Model Browser, but the other one does.
I have no idea why this is, has anyone faced this problem before?
No matter how many times I start over, I can't get it to work.
I have my app using core data with the data model below. However, I'm switching to a standard database with columns and rows. Can anyone help me with setting up this new database schema?
First of all you need to create tables for each of the Entities and their attributes (note I added "id" to each of the tables for relationships):
Routine (name, timestamp, id)
Exercise - this looks like a duplicate to me, so leaving one only here (muscleGroup, musclePicture, name, timeStamp, id)
Session (timeStamp, id)
Set (reps, timeStamp, unit, weight, id)
Now that you have tables that describe each of the entities, you need to create tables that will describe the relationships between these entities - as before table names are in capitals and their fields are in parenthesis:
RoutineExercises (routine_id, exercise_id)
SessionExercises (session_id, exercise_id)
ExerciseSets (exercise_id, set_id)
That's it! Now if you need to add an exercise to a routine, you simply:
Add an entry into Exercise table
Establish the relationship by adding a tuple into RoutineExercises table where routine_id is your routine ID and exercise_id is the ID of the newly created entry in the Exercise table
This will hold true for all the rest of the relationships.
NOTE: Your core data model has one-to-many and many-to-many relationships. If you want to specifically enforce that a relationship is one-to-many (e.g. Exercise can only have 1 routine), then you will need to make "exercise_id" as the index for the RoutineExercises table. If you want a many-to-many relationships to be allowed (i.e. each exercise is allowed to have multiple routines), then set the tuple of (routine_id, exercise_id) as the index.
I've a problem mapping just one table from database, I add several tables using "Update model from Database" function through Visual Studio 2010 interface, and everyone works as expected except one table!
Looking at "Model Browser" I can see the table doesn't appear under "Entity Types" but it is present under section "ObjectEntity.Store", so my POCO Generator create an entity related and I can't try to add it again from database but I can't access it through context (like context.table_name).
Tha table doesn't have particular form, there are just two key fields
Could someone help me?
Thanks
I guess it is junction table for implementing many-to-many relation, isn't it? In such case it is correct behavior. EF will hide this table because it is not needed in object oriented approach where many-to-many association can be modeled directly without helper entity. You will see in your model that those two related entities are connected by line with * - * multiplicity and each entity will contain navigation property which is collection of related entities. By manipulation with entities in these collections you are creating or removing records in that hidden table. That is the way how you work with such relation in EF.