I have a very basic student model property,
public int ID { get; set; }
which is auto incrementing and identity. I want to add more value with it. Which will end up like,
department id + batch id + its own auto-incremented value
Should I disable its identity? I want it to be auto generated. How can I handle that and where (Model, View or Controller)?
You can't update pmk in EF
You should never update the pmk of a table anyway. If you want to auto generate a pmk for a field, simply use a random number for each student.
There are a couple of approaches you could take with designing your table...
One would be to remove the auto increment and add your own value to the record.
Pros: You have full control over the id you're going to insert.
Cons: Concurrency is going to be an issue in that another process could have already written the ID you are about to write. Also you'd still have to keep a running counter somewhere or parse existing record ids.
Another approach is to create an additional identifier field on your table that you can populate based on the combined values you want.
Pros: The database is handling the incrementing identity fields for you.
Cons: You will have to make more than one call to the database to insert a new record. Assuming the deptid and batchid are not in the table (so you can't use a trigger) then you'll have to insert, get the identity, then run an update statement to populate the new identifier field.
Of course, you can always have Departments and Batches in separate tables with foreign keys in your Students table. The data is still preserved and you can use joins for reporting or whatever you need rather than parsing out identifier fields.
As for where this code belongs... that depends on the architecture of your application. If you have a nice repository then you could encapsulate that logic within your insert/create function. If not, then I'm afraid the controller is probably where you're going to have to keep this logic, which will be a little messy.
Hope this helps and good luck!
Related
I have one master & detail in my 'db1' and there is one column named 'EntryByUserId' in master table.
User table is available in 'db2'.
When all the tables are available in one single database we can directly get user detail by using include function. But here my reference table is in another database so in my case user object will return null value. So anyone please help me to achieve this.
I have created multiple dbcontext in my project but don't know how to get this.
Below is the code we use when all tables are available in single database.
dbcontext1.tbl_Master.Include(m => m.tbl_Detail).Include(m => m.tbl_user)
.AsNoTracking().FirstOrDefault();
One option to accommodate this cleanly, especially for something as frequently accessed as a "User" reference for something like reporting on CreatedBy or ModifiedBy tracking on rows would be to implement a view within Db2 that lists the users from Db1. Then in your main application context you can map a User entity to the view rather than a table. I would put guards in your DbContext and entities to discourage/prevent modifications to this User entity, and leave maintenance of users to a DbContext overseeing the Db1 tables.
If this is something like a multi-tenant system with a system database for authentication and separate DBs per tenant which are tracking things like CreatedBy against records, I would recommend considering a system to inspect and replicate users between the auth database and the respective tenant databases. The reason for this would be to help enforce referential integrity for the data and the user references. The issue with the view approach is that there is no constraint available to ensure that a UserId reference actually corresponds with a row in the Users table over in the other database. It can be indexed, but not constrained so you have to handle the possibility of invalid data.
As an example:
I have two tables in firebird:
TB_CUSTOMER
IDCUSTOMER (autoincrement generator)
CUSTOMERNAME
TB_PHONE
IDPHONE
IDCUSTOMER (foreing key from TB_CUSTOMER)
PHONE
I have a registration form developed in Delphi. The table data TB_PHONE are handled using a dbgrid. I can not assign the value of the field IDCUSTOMER in TB_PHONE, because it was not generated by the Firebird generator. How can I make the relationship between the tables? I want to implement it without first saving the table data TB_CUSTOMER. I'm using datamodules with IBDAC.
Any sugest?
Before detail table can be inserted into, you should have PK-index over master-table updated and having proper master-ID in it. That means that some piece of code should insert master-record before inserting detail-record. Where this piece of code would be - is only limited by your fantasy.
Few arrangements include
insert the master-row in your application. Read the id of the row. Insert detail-row using this id.
read ID from then Generator, then insert both rows (master 1st) using the obtained ID
create a stored procedure, inserting both rows and returning ID (implementing #1 or #2 server-side)
use EXECUTE BLOCK - basically ad hoc anonymous SQL procedure. But that only is available in FB 2.x and except for not using namespace it is inferior to #3.
add BEFORE INSERT trigger onto detail table, searching for ID in master and adding one if not found. This would slow down all insert operations (even when master-ID already exists - that should be checked), would not be able to fill all other master columns but ID and is potentially dangerous due to hiding application logic problems. But still that can be implemented (though ugly and dirty method)
create master-join-detail VIEW and add INSERT trigger for it, propagating the new view-row into both master-table and details-table.
et cetera
I want to implement it without first saving the table data TB_CUSTOMER
There's your problem. You need the primary key from the master table before you can save the detail. That's just the way it works. But if what you want is to make sure that the values get saved together, you can do that as a transaction. In Firebird, you can do it like this:
Begin a transaction. Exactly how you do that depends on which DB library you're using to access your Firebird database.
Run an INSERT INTO ... RETURNING statement to insert the row into your master table and retrieve the generated value as a single operation.
Use the generated PK value to fill in the FK value on your detail table.
Insert the detail row.
Commit the transaction.
Say I have a generic repository interface as follows:
public interface IRepository<T>
{
Add(T item);
Delete(int itemId);
Update(T item);
}
Typically the new ID of an item added through IRepository.Add() would be determined by some back-end database, but only once the overall transaction/unit of work has been submitted. So I'm fairly certain that it would be wrong for IRepository.Add() to return the new ID of the added item. The repository really shouldn't know anything about how ID are created. Is this correct?
If this is a case how else can one determine the new ID of an item added to a repository, or should I even be doing this? I know an ORM like NHibernate is able to automagically replace objects in memory with new objects with the correct ID, but I'm trying to design my repository with out any specific ORM implementation in mind.
For example say I have a website where customers can make orders. A new customer chooses to check out and is sent to a form to fill out their details. This information is used to create a Customer object which is stored in a CustomerRepository. Now their order information needs to be created but an Order needs to reference a Customer by their ID?
Customer newCustomer = new Customer(first, last, address, phone dateOfBirth);
customerRepository.Add(newCustomer);
//How would I determine customerId??
Order newOrder = new Order(customerId, shippingAddress, billingAddress);
newOrder.AddOrderItem("widget");
newOrder.AddOrderItem("doohicky");
newOrder.AddOrderItem("stuff");
In the example you give, I would create the Customer and Order in one step, and pass domain objects to domain objects, instead of passing Ids:
Customer newCustomer = new Customer(first, last, address, phone dateOfBirth);
// Pass the customer rather than the CustomerId:
Order newOrder = new Order(newCustomer , shippingAddress, billingAddress);
newOrder.AddOrderItem("widget");
newOrder.AddOrderItem("doohicky");
newOrder.AddOrderItem("stuff");
customerRepository.Add(newCustomer);
orderRepository.Add(newOrder);
// SaveChanges()
...when the changes are saved, the framework automatically populates the Ids of both Customer and Order, and fills in Customer.Id, Order.customerId, (etc.) by virtue of the Customer object having been assigned to the Order.
Eric,
In the scenario you mention, I don't see any CommitChanges() going on. I would wrap everything in a transactionscope and then hit customerRepository.CommitChanges() before you add the orderlines. you should then be able to grab the id from the newly created customer object and use it as follows:
Order newOrder = new Order(newCustomer.Id, shippingAddress, billingAddress);
then, if the order(s) fails, you can roll everything back and keep it atomic by not hitting scope.Complete().
hope this helps..
I generate id on a client (a la CombGuid.NewGuid()) and then pass it to constructor. Approach when you are using database identity has serious disadvantages
Whether or not you use NHibernate, I feel that the approach it takes is the right one. Your goal with any domain objects is to only ever have one instance of that object in memory at any one time, i.e. you should never have two objects that represent the same database record. It follows that if the database has updated the record with a new id, the domain object in memory should also be updated with that ID since that is the "one" true representation of that record.
After calling Add, the object's ID is set and you could then make further changes to that object and call Update without having to know too much about your implementation.
Your interface is more DAO than Repository according to DDD:
http://codebetter.com/iancooper/2011/04/12/repository-saveupdate-is-a-smell/
Like Steve Wilkes mentioned, you should keep reference of Customer in Order and not Customer Id so when Unit of Work is processed, it will create correct link those Entities in Persistence Storage (SQL DB, Web Service etc)
For more on DAO here: http://java.sun.com/blueprints/corej2eepatterns/Patterns/DataAccessObject.html
Domain entities should have their own ID strategy regardless database IDs, so preferably generate your id in the domain layer, or if you really need to generate id in database, then add another domain identifier generated at domain layer beside the database auto generated id.
In domain driven design where you apply repository pattern you should not tie your domain with database so relying on database for id creation is not a good idea.
Another point is that you may want to make customer associated in order not just putting the customer id, this makes the domain layer rich and solid.
I have asp.net membership and I use the built in Create user method since it is convenient now after this depending on the user I want to add 2 more fields to the aspnet_UserTable.
In my aspnet_user Table I have like this
// All Standard Fields that come with this table
ClubID<nullable)
ClubName <nullable)
I have a table that relates this
Club Table
ClubID<PK>
ClubName
So this relationship forms that one club can have many users. But one user can only have 1 club.
So now I been trying to figure out how to add the ClubID to the aspnet Usertable since it does not show up in the Entity Framework Diagram since it does not show FK.
// Note in this case I am just using EF made to create but in reality I will use the Membership.Create.
aspnet_Users test = aspnet_Users.Createaspnet_Users(Guid.NewGuid(), Guid.NewGuid(), "myTest5", "mytest5", false, DateTime.Now);
test.Club = Club.CreateClub("One224", "Two224");
test.ClubName = "go";
MyEntities.AddToaspnet_Users(test);
MyrEntities.SaveChanges();
So what I have works but it just makes no sense and I hope there is a better way. Like I try to create the club and then stick it in the test.club.
This add's the ClubID primary key but does not add the clubName.
So then I have to add the club name separately. Like why? Is there not a better way?
I also prefer linq method syntax so if it is needed and you know this syntax can you please write it in that.
I would recommend a few things.
One: Strongly consider not adding columns to the aspnet_* tables. If you ever want to change your authentication method down the road you'll be stuck lugging those tables around with you even though you won't need them anymore. Also, there may be a new, better version of the membership provider one day that you won't be able to upgrade because you have customized the membership schema.
Two: Instead, why not create a new table called User (or something of your liking) that has your own primary key but links back to the ASP.NET Membership unique key (the guid).
Your table might look like
User
UserId (PK)
AuthenticationUserId (FK back to aspnet_User table)
ClubId (FK back to your club table)
Three: I don't understand why you've repeated ClubName both in your user table and in your Club table. You really only need to define the ClubName once, right? Keep your Club table how it is but remove the ClubName column from the user table.
Your code above for associating the club with the user is correct and works because that's how the Entity Framework works. You're associating entities with each other and are abstracted from some of the relational aspects of your data schema. It's a little strange to get used to it first but it does work.
I want to use an example to explain what I want.
Assume I've following DB design:
Item (id, name, categoryID);
Category (id, name);
When user wants to create an Item (fill in form), I'll give a list of categories in a dropdownlist, and when user chooses one of the categories ASP.NET MVC will automatically bind categoryID, to the selected one. I need to present same dropdown list when editing the item with correct selected one.
Question:
But my DB is very big, and it requires around 30-40 (maybe even more) category-like tables, that contain just "id" and "name", and all tables need to be shown in dropdown list while creating some other object, and also needs to be presented while editing the object. Definitely above schema doesn't work, because it's tedious to write same logic 100 times with just different table names. (I'm using Linq2SQL)
Currently my solution is:
Make a view that's based in all such tables and in application I just call a function that construction dropdownlist from that single view. But it's still tedious to change view definition everytime I add a new table.
Do you guys think of a better solution for this tedious work, possibly using reflection or some other tecnologies.
It is not a problem "Definitely above schema doesn't work, because it's tedious to write same logic 100 times with just different table names."
If I were you, I will mark an addition interface on these class using "partial class" feature.
Then, I will write few extension method for the partial class.
If anyone interested in the solution:
I've used reflection to solve this problem.
I use reflection over DataContext to get the Table (by string name), and get its fields and construct the optionlist.