I am using entity framework and developing an architecture for application with remote data access. Coming back to point, i query the database for one record (say on the basis of itemcode). Now the resultset i will get whether i should return it as List or collection or simple as an object of entity. I am using entity object but my boss is saying i should use List. He thought , returning result as an entity with return whole table structure also. Quick suggestion would be appreciated.
List<Employee> lstemployee = GetRecordByCode(itemCode)
or
Employee emp = GetRecordByCode(itemCode)
What's the difference? If itemCode is a unique key you will either get one Employee object or a list containing the same one Employee object. You will never return the whole table. That will only happen if within GetRecordByCode you do something like context.Employees.ToList() without any Where filter before the ToList().
If itemCode is not unique you even have to use a list.
Related
We have identified a Location entity in a database as a value object in our domain (DDD). Locations are used by other domain objects, but don't really "stand alone" -- they always belong to another entity.
Now we are trying to edit a list of these values in a simple MVC web application. So the view would show a list of locations in a view model LocationViewModel.
However, the value object is by definition immutable, yet does hold a reference to another entity (Business).
Domain:
public class Location : ValueObject<Location>
{
readonly locationId;
public int LocationId {get{return _locationId;}}
public Business Business {get;set;}
}
My problem is understanding how you can simply edit a bunch of value objects in a UI and change, e.g. what Business the location belongs to.
A value object is not supposed to have an "identity", but it does need an ID so the repository can update the database.
I also don't think you can make Location an entity just because you want to edit it in the UI. Or is Location, in this scenario indeed an Entity?
What am I not understanding?
Thank you!
It's a classic problem. In one context it's an entity and in another a value object. I found the example of a telephone number helpful to understanding this sort of problem.
In a CRM for example, a telephone number is a value object. The same one can be associated with multiple contacts. It varies by value (key concept here). So in this context it's a value object. In this example, I could store telephone numbers in the database and the 'ID' would be the telephone number itself. If the value object was made up of multiple parts then they would form a composite key.
If however we looked at a telephone number at a telephone company. That would most likely be an Entity. It could have all manor of information attached to it. All that info would vary by ID (which in this case would be the number).
In your case, Location sounds like a value object. If you need to save it in a database as a thing rather than just as part of an entity then use it's parts as a composite key. You will need to handle what happens when you 'change' one as it's not a change but the creation of new value object. One approach is to remove the old and insert the new. Or just keep all versions. It depends on your domain.
Hope that's helpful.
You don't change a value object. You create a new one with different values. If the value object has few properties that you want often to change, some helper methods are usefull. myObject.WithX(4711) will create a new instance with all properties the same as myObject but the X Property changed to 4711 for example.
To "edit" a value object in an UI you use a viewmodel. The Viewmodel is not a value object (and no entity by the way) and is not part of your domain. It's purely in the Presentation Layer. It is editable and mutable. It could have a constructor, taking your (immutable) value object to copy its values from and it could have a ToXXX Method to create a new (immutable) value object with its current (and changed) values.
If you want to store your value objects in a separate table (instead of roll out the fields in the table that stores the owning entity) this is purely data access layer related and not part of your domain model. This could be done by mapping. In the value object the database id is immutable and has no meaning in the domain model.
Supposed I have an online store and a model User, which contains a whole bunch of parameters (First Name, Last Name, an Address object, ProductCategoryAccess object etc.)
The way it's currently set up is the constructor accepts an Id and populates the entire class with data from the database.
But what if I don't need all that data? For example, if I have a view that just lists users, I'd have to create a list of Users, with each of them needlessly querying the database for information that I don't need (Address, ProductCategoryAccess, etc).
What's the best way of handling this? Do I create a bunch of different classes, with only the parameters I need for various situations? Do I create one User class, but with different "setter" methods, which will use different queries to populate only certain parameters?
Are you using any ORM tools to get the data? If yes, then you could use lazy binding to retrieve only elements that you need.
If you are directly querying the db, then dividing it across different methods with queries should do the trick.
What are the different situations you need to account for?
If you only wish to select certain properties from your user database record then you can use projections to bind the records into a data transfer object that contains only the properties you need for any given page.
For instance, if you needed properties for an edit user page then your query (I assume you're using Entity Framework?) would look something like this:
this.userContext.Users.Where(y => y.UserId == userId).Select(x => new UserEditDto {
FirstName = x.FirstName,
Surname = x.Surname,
EmailAddress = x.EmailAddress
}).FirstOrDefault();
What this will do is build a LINQ query against the database that selects only the properties specified within the select part of the LINQ statements. In fact, if you were to remove the FirstOfDefault() method and stick a breakpoint in you'd be able to see the SQL generated by that statement would look a little something like:
SELECT FirstName, Surname, EmailAddress FROM users WHERE userId = 1;
It's only when you call .FirstOrDefault() does the LINQ provider execute the query against the database and return the result.
From here you're able to return your DTO to your service layer or your controller to send it to a view within a view model. You can then rinse and repeat this same type of query for other possible data transfer objects and views that require certain data.
In the cache, I've got an Entity of type 'Mandate'.
Then I run the following code to fetch a collection of MandateHistory entities, which is then merged by breeze to the corresponding property of the Mandate entity :
function getMandatHistory(mandatId) {
var query = breeze.EntityQuery.from("MandatesHistory")
.where("Mandate.Id", "==", mandatId).orderBy("Id")
.expand("Mandate").skip(offset).take(pageSize).inlineCount(true);
return manager.executeQuery(query.using(service));
}
Note the orderBy clause is respected and the results are properly sorted by Id.
However the items in the collection property of the Mandate entity is NOT sorted. Do I have to do something special here ?
Sorting of the values returnd by collection navigation properties is NOT something that Breeze does. It will sort the results of a query, but if you want to sort, ( and keep sorted), one of the collection properties of an entity you will need to manage that yourself.
I think your best two options are either.
1) Sort before display. i.e. call a sort method on any collection right before you display it. Depending on what MVVM framework you are using, there is often a 'binding' that does exactly this.
2) Subscribe to the Breeze arrayChanged event on the array returned by your navigation property and call sort on the array anytime you see the change event. Note this can get expensive if you subscribe to a lot properties on a lot of entities.
I have created a database using the edmx designer in an ASP.NET MVC project. This has a number of tables like this:
An Office can have many Locations
Each Location can have many Staff
Each Location has Location Type
Each Location has a Business Type
Each Location has a Browser Version
Each Browser Version has a Browser
The details of this are probably unimportant. The core class is Staff, it has a Location property, which has an Office property, a LocationType property, a BusinessType property and a Browser Version property (which has the Browser property).
I'm creating a registration form. I started by trying to create a Staff member instance to save by using code like staffMember.Location.LocationType = DB.Locations(l => l.Id = model.Id);
which populated the class with fully populated class instances. Calling the save method at this point would blow up with :
Entities in 'DBContainer.BrowserVersions' participate in the
'BrowserBrowserVersion' relationship. 0 related 'Browsers' were found.
1 'Browsers' is expected.
Now, again, the BrowserVersion.Browser class was correctly populated.
So, I did some reading, and as a result I made sure my code always uses the same DBContext. This did not fix my issue. So I changed my code to do something like this:
staffMember.Location.BrowserType = new BrowserType { Id = myBrowserType.Id };
This would then blow up with an error like :
{"Cannot insert the value NULL into column 'BrowserName', table
'MyProject.dbo.Browsers'; column does not allow nulls. INSERT
fails.\r\nThe statement has been terminated."}
In the end I found I cannot use the objects copied from my DBContext, but I need to create objects that have all the relevant properties copied across from the objects I get from the DB. Surely I am doing something wrong, I'm writing more code now than if I used stored procs and my own data layer?
I have a Client entity and PostCode entity in Linq to SQL model. The Clients table in database contains client_postcode column which is a FK column to postalcode column in PostCode table, which is a varchar column primary key for PostCode table.
When updating Client, in my code I do this
// postcode
updating.PostCode = (from p in ctx.PostCodes
where p.postalcode.Equals(client.PostCode.postalcode)
select p).First();
where client object is provided from ASP.NET MVC View form. This code seems to set the PostCode related entity fine. But when calling SubmitChanges() I receive the following exception:
Value of member 'postalcode' of an object of type 'PostCode' changed. A member defining the identity of the object cannot be changed. Consider adding a new object with new identity and deleting the existing one instead.
So I am currently unable to change the related entity. How is that done in Linq to Sql?
UPDATE:
After further review and troubleshooting I found out that the problem is in ASP.NET MVC UpdateModel() call. If I call UpdateModel() to update the existing entity with the edited data, something is wrong with the FK assignement for PostCode. If I don't call UpdateModel and do it by hand, it works.
Any ideas what goes wrong in UpdateModel() that it can't set the relationship to foreign key entities correctly?
I am updating this question and starting a bounty. The question is simplified. How to successfully use L2S and UpdateModel() to work when updating items (with related entities as FK) in ASP.NET MVC Edit views?
It seems to me that you are receiving PostCode.postalcode in the http post request.
Based on how model binding works, the UpdateModel call updates .PostCode.postalcode of the model you are passing to it.
Use this overload to include or exclude specific properties.
Wouldn't updating.client_postcode = client.client_postcode; accomplish what you want?
Client.PostCode should be looked up on seek based on client_postocde.
You can not do what you are trying, you cannot change the Postcode like that.
James' idea is in the right direction.
Updatemodel() takes the matching values from the Formcollection
How do these values come in the Formcollection? What are their keys?
basically there are 2 ways in editing an object.
option 1:
all the value names you want to update have corresponding keys in the Formcollection, which leaves you just to call UpdateModel() of the original object. do SubmitChanges()
option 2:
Get the original object, change it's values manually (because the keys dont correspond) and do SubmitChanges()
you are tying to change a link, you cant do that. you can only edit the updating.client_postcode which in this case is a string?
Can you please copy the whole action here? So I can write some code for you without gambling.