The question could also look like "Why is my initialization code of object in server not working?".
For example,
public class Order
{
public int Id { get; set; }
public int Quantity { get; set; }
public Order()
{
Quantity = 10;
}
}
From debugger, I can see the contructor is called and Quantity is set, however, it is not taking effect. I have to set Quantity on client side after the entity is created to make it work.
Is there a way to make the initialization on server work? By the way, my project is in Angular/Breeze/EF.
UPDATE: As I dig a little further, I believe, this is the general "issue" with Breeze that the server side change must be added to so-called entityInfo.OriginalValueMap, otherwise, its change is not saved. If true, how can work around this limitation because I have a lot default values I'd like to set on server?
This is how I create my entity:
var manager = new breeze.EntityManager("breeze/breeze");
manager.enableSaveQueuing(true);
function _createEntity(entityName) {
return manager.createEntity(entityName);
}
Setting any initialization code on the server in the model constructor won't work simply because the JavaScript client doesn't know anything about the C# constructor code on the server.
The DefaultValueAttribute is only honored when you're constructing a Model-First metadata. It is unfortunately ignored by EF when constructing a Code-First model metadata.
I suggest that you see Breeze - Create Entity on Server side for how another user solves a similar situation by creating a "create Endpoint" on the server that basically returns a new entity with default values set.
You don't have to create a constructor to set default values.
Just add the default value data annotation to any property you wish to set its default value:
[DefaultValue(10)]
public int Quantity { get; set; }
Also, consider not to initialize the Quantity when creating an entity at the client side.
Related
I am having trouble when trying to delete a field of an Entity using Entity Framework (version 6.1.3).
Let's say I have two Entities: Person and Work.
I can change the work of a person without any issue, but when I try to express that the person is unemployed it does not work properly:
person.Work = null;
db.SaveChanges();
After running this code the person still will have the previous work, but if I use the debugger and check the Work property of person before running
person.Work = null;, everything will behave as expected.
Can someone please explain why reading the value first makes the code work properly and how to correctly delete the field?
var work = person.Work; \\ with this line here everything works as expected
person.Work = null;
db.SaveChanges();
Two things that are contributing to your issue:
Entity Framework determines what needs to updated during SaveChanges by tracking changes to property values.
You probably have lazy loading enabled (both in general and for the Work property), which means that if the person has an associated Work, that associated entity doesn't get loaded until the first time you access that property.
Putting those together, when you set person.Work = null without accessing person.Work (which would trigger a load), the context thinks nothing has changed. But if you load the property first, setting the property to null tells EF to remove that association. Edit: According to the page that octavioccl linked, this is true for .NET 4.0., but for .NET 4.5+ (and EF 5+), loading first is unneeded.
Possible solutions
If you want to remove the association without loading the related entity, you'll need to add a foreign key property to your Person entity, then you can set that to null instead of setting the navigation property to null. For example:
public class Person
{
// other properties...
public int? WorkId { get; set; }
public virtual Work { get; set; }
}
person.WorkId = null;
db.SaveChanges();
octavioccl's answer quoted another option:
context.Entry(person).Reference(p => p.Work).CurrentValue = null;
From this msdn page:
To delete the relationship, set the navigation property to null. If
you are working with the Entity Framework that is based on .NET 4.0,
then the related end needs to be loaded before you set it to null. For
example:
context.Entry(person).Reference(p => p.Work).Load();
person.Work = null;
Starting with the Entity Framework 5.0, that is based on .NET 4.5, you
can set the relationship to null without loading the related end. You
can also set the current value to null using the following method:
context.Entry(person).Reference(p => p.Work).CurrentValue = null;
I have a web api project that I'm building on an N-Tier system. Without causing too many changes to the overall system, I will not be touching the data server that has access to the database. Instead, I'm using .NET remoting to create a tcp channel that will allow me to send requests to the data server, which will then query the database and send back a response object.
On my application, I would like to use entity framework to create my datacontexts (unit of work), then create a repository pattern that interfaces with those contexts, which will be called by the web api project that I created.
However, I'm having problems with entity framework as it requires me to have a connection with the database. Is there anyway I can create a full entity framework project without any sqlconnections to the database? I just need dbcontexts, which I will be mapping my response objects and I figure that EF would do what I needed (ie help with design, and team collabs, and provide a nice graphical designer); but it throws an error insisting that I need a connection string.
I've been searching high and low for tutorials where a database is not needed, nor any sql connection string (this means no localdb either).
Okay as promised, I have 3 solutions for this. I personally went with #3.
Note: Whenever there is a repository pattern present, and "datacontext" is used, this is interpreted as your UnitOfWork.
Solution 1: Create singletons to represent your datacontext.
http://www.breezejs.com/samples/nodb
I found this idea after going to BreezeJS.com's website and checked out their samples. They have a sample called NoDb, which allows them to create a singleton, which can create an item and a list of items, and a method to populate the datacontext. You create singletons that would lock a space in memory to prevent any kind of thread conflicts. Here is a tid bit of the code:
//generates singleton
public class TodoContext
{
static TodoContext{ }
private TodoContext() { }
public static TodoContext Instance
{
get
{
if (!__instance._initialized)
{
__instance.PopulateWithSampleData();
__instance._initialized = true;
}
return __instance;
}
}
public void PopulateWithSampleData()
{
var newList = new TodoItem { Title = "Before work"};
AddTodoList(newList);
var listId = newList.TodoListId;
var newItem = new TodoItem {
TodoListId = listId, Title = "Make coffee", IsDone = false };
AddTodoItem(newItem);
newItem = new TodoItem {
TodoListId = listId, Title = "Turn heater off", IsDone = false };
AddTodoItem(newItem);
}
//SaveChanges(), SaveTodoList(), AddTodoItem, etc.
{ ... }
private static readonly Object __lock = new Object();
private static readonly TodoContext __instance = new TodoContext();
private bool _initialized;
private readonly List<TodoItem> _todoLists = new List<TodoItem>();
private readonly List<KeyMapping> _keyMappings = new List<KeyMapping>();
}
There's a repository included which directs how to save the context and what needs to be done before the context is saved. It also allows the list of items to be queryable.
Problem I had with this:
I felt like there was higher maintenance when creating new datacontexts. If I have StateContext, CityContext, CountryContext, the overhead of creating them would be too great. I'd have problems trying to wrap my head around relating them to each other as well. Plus I'm not too sure how many people out there who agree with using singletons. I've read articles that we should avoid singletons at all costs. I'm more concerns about anyone who'd be reading this much code.
Solution 2: Override the Seed() for DropCreateDatabaseAlways
http://www.itorian.com/2012/10/entity-frameworks-database-seed-method.html
For this trick, you have to create a class called SampleDatastoreInitializer that inherits from System.Data.Entity.DropCreateDatabaseAlways where T is the datacontext, which has a reference to a collection of your POCO model.
public class State
{
[Key()]
public string Abbr{ get; set; }
public string Name{ get; set; }
}
public class StateContext : DbContext
{
public virtual IDbSet<State> States { get; set; }
}
public class SampleDatastoreInitializer : DropCreateDatabaseAlways<StateContext>
{
protected override void Seed (StateContext context)
{
var states = new List<State>
{
new State { Abbr = "NY", Name = "New York" },
new State { Abbr = "CA", Name = "California" },
new State { Abbr = "AL", Name = "Alabama" },
new State { Abbr = "Tx", Name = "Texas" },
};
states.ForEach(s => context.States.Add(s));
context.SaveChanges();
}
}
This will actually embed the data in a cache, the DropCreateDatabaseAlways means that it will drop the cache and recreate it no matter what. If you use some other means of IDatabaseInitializer, and your model has a unique key, you might get an exception error, where you run it the first time, it works, but run it again and again, it will fail because you're violating the constraints of primary key (since you're adding duplicate rows).
Problem I had with this:
This seems like it should only be used to provide sample data when you're testing the application, not for production level. Plus I'd have to continously create a new initializer for each context, which plays a similar problem noted in solution 1 of maintainability. There is nothing automatic happening here. But if you want a way to inject sample code without hooking up to a database, this is a great solution.
Solution 3: Entity framework with Repository (In-memory persistence)
I got this solution from this website:
http://www.roelvanlisdonk.nl/?p=2827
He first sets up an edmx file, using EF5 and the code generator templates for EF5 dbcontexts you can get from VS extension libraries.
He first uses the edmx to create the contexts and changes the tt templates to bind to the repository class he made, so that the repository will keep track of the datacontext, and provide the options of querying and accessing the data through the repository; in his website though he calls the repository as MemoryPersistenceDbSet.
The templates he modified will be used to create datacontexts that will bind to an interface (IEntity) shared by all. Doing it this way is nice because you are establishing a Dependency Injection, so that you can add any entity you want through the T4 templates, and there'd be no complaints.
Advantage of this solution:
Wrapping up the edmx in repository pattern allows you to leverage the n-tier architecture, so that any changes done to the backend won't affect the front end, and allows you to separate the interface between the front end and backend so there are no coupled dependencies. So maybe later on, I can replace my edmx with petapoco, or massive, or some other ORM, or switch from in-memory persistence to fetching data from a database.
I followed everything exactly as explained. I made one modification though:
In the t4 template for .Context.tt, where DbSetInConstructor is added, I had the code written like this:
public string DbSetInConstructor(EntitySet entitySet)
{
return string.Format(
CultureInfo.InvariantCulture,
“this.{1} = new BaseRepository();”,
_typeMapper.GetTypeName(entitySet.ElementType), entitySet);
}
Because in my case I had the entityset = Persons and entityname = Person. So there’d be discrepancy. But this should cover all bases.
Final step:
So whether you picked solution 1, 2, or 3. You have a method to automatically populate your application. In these cases, the stubs are embedded in the code. In my case, what I've done is have my web server (containing my front end app), contact my data server, have the data server query the database. The data server will receive a dataset, serialize it, and pass it back to the web server. The web server will take that dataset, deserialize it, and auto-map to an object collection (list, or enumberable, or objectcollection, etc).
I would post the solutions more fully but there's way too much detail between all 3 of these solutions. Hopefully these solutions would point anyone in the right direction.
Dependency Injection
If anyone wants some information about how to allow DI to api controllers, Peter Provost provides a very useful blog that explains how to do it. He does a very very good job.
http://www.peterprovost.org/blog/2012/06/19/adding-ninject-to-web-api/
few more helpful links of repository wrapping up edmx:
http://blogs.msdn.com/b/wriju/archive/2013/08/23/using-repository-pattern-in-entity-framework.aspx
http://www.codeproject.com/Articles/688929/Repository-Pattern-and-Unit-of
I have published a WebAPI service which returns a list of items. I am implementing Breeze and have managed to get it basically working with filtering/sorting. However, the Expand is not working.
http://www.ftter.com/desktopmodules/framework/api/dare/dares?$expand=ToUser
You can see the ToUserId ForeignKey in the response above, but the ToUser properties are NULL (the user definitely exists)
You can see the ToUser EF navigation property in the metadata.
When I use .Include on the server side I can populate it with EF, but I don't want to do this.
I checked the Breeze Tutorial 2 here on Expand: http://learn.breezejs.com/
Here is it without expand: http://learn.breezejs.com/api/northwind/Products
and here it is with Expand (And you can see the additional Category info): http://learn.breezejs.com/api/northwind/Products?$expand=Category
This is what I am trying to do but mine does not fill it...
UPDATE:
I downloaded the Breeze 1.3.6 Samples and loaded the DocCode solution in VS2011.
I ran it and saw that the client-side expand works;
e.g.
http://localhost:47595/breeze/Northwind/Orders?$top=1 (no expand)
http://localhost:47595/breeze/Northwind/Orders?$top=1&$expand=Customer (expands customer correctly).
I checked the WebAPI controller code and it looks the same, except they use EF Code First instead of Model First. The Foreign key is decorated with a property:
Breeze Sample that Works
[ForeignKey("CustomerID")]
[InverseProperty("Orders")]
public Customer Customer {get; set;}
It just doesn't make sense... it is something to do with my WebAPI controller or EntityFramework relationship...
UPDATE 2
I downloaded the most basic ToDo Knockout Breeze sample and added this line to the ToDoItem class: public User ToUser { get; set; }
I am then able to Expand the WebAPI call with http://localhost:63030/breeze/todos/Todos?$expand=ToUser
So I have come to the conclusion that it is something to do with the fact that I am using EntityFramework DB First and not Code First. It definitely does seem possible to do in the current version of the WebAPI with Breeze and EF.
UPDATE 3
I have narrowed it down to my database, EF Database First and Code First differences, but still not identified the issue. I have changed from a Model to a Code First approach with the exact same result (ie. no expand).
For example: if you look at this Expand on the Breeze site that works, http://learn.breezejs.com/api/northwind/Products?%24expand=Category, try change the last param to an invalid field and it throws an error, e.g. :
http://learn.breezejs.com/api/northwind/Products?%24expand=Category1
However, in my code, it always ignores this param and returns ALL the records, and never throws an exception if the Expand param is incorrect:
http://www.ftter.com/desktopmodules/framework/api/dare/dares?$expand=To4657657User
Hence I am stumped.. I have no idea why this is not working.
My Code
[HttpGet]
[Queryable(AllowedQueryOptions = AllowedQueryOptions.All)]
public HttpResponseMessage Dares()
{
var response = Request.CreateResponse(HttpStatusCode.OK, (IQueryable<Dare>)contextProvider.Context.Dares);
return ControllerUtilities.GetResponseWithCorsHeader(response);
}
and here is the generated class from my EF model (using Database First)
public partial class Dare
{
public int DareId { get; set; }
public int ToUserId { get; set; }
public virtual User ToUser { get; set; }
}
Your URL seems to be missing the $ for the expand query option...should be $expand.
I think I have found the problem - the IQueryable with the HttpResponseMessage return type does not behave the same as a pure IQueryable return type. expand seems to work when I do not wrap it.
I have raised a new question here:
How to use Breeze IQueryable with CORS?
I am using DB First EF 4.1 and I am adding DbContextGenerator tt template to my model. This is all great, but I end up with classes like this:
public partial class t_city
{
public t_city()
{
this.t_neighborhood = new HashSet<t_neighborhood>();
}
public int city_id { get; set; }
public string city_name { get; set; }
public virtual ICollection<t_neighborhood> t_neighborhood { get; set; }
}
This is super ugly. I modified the template to generate properties in camelcase, but that breaks the mapping onto tables and columns. Is there way to get clean class names and still preserve the mapping?
EDIT
Looks like it's possible by renaming the objects inside the Entity Model file. The only question remains, is it possible to automate the renaming using a function, or does it have to be done manually each time?
Thanks!
You need to do it manually but that's needed only once for each entity / property. These changes are not deleted when you update your model from the database.
The only automation can be implemented as some processing of EDMX file. It is XML with defined schema so you can process that XML in your custom tool or XSLT transformation and automatically change property and entity names in CSDL and MSL.
I'm using Entity Framework 4 and a Dynamic Data site to expose a bare-bones admin interface to a few users. Working pretty well in general, but I have run into this one problem on a couple of fields on my model.
Several tables have some audit-related fields - CreatedBy, CreatedDate, ModifiedBy, and ModifiedDate. These fields are required in the database and the associated models are marking the properties as non-nullable (all as it should be). However I am handing setting the values for these fields in code - the field templates for the field types mark these specific fields as disabled on the page, and in the SavingChanges event I set these fields to the appropriate values. All works great when I'm updating an existing item.
The problem comes in when I try to create a new item. I want these fields to remain empty on the page and be auto-populated by my code when submitted, but the Field Templates set up RequiredFieldValidators for these fields and won't let me submit them without a value. Normally this would be great, except that I want to prevent EF from validating these fields at the point of page submission.
I realize that I could mark the fields as nullable in the database and that would resolve the issue - it would probably even be just fine from the data standpoint, but I'm not comfortable with doing so - for one thing it's not unlikely that some of the models these fields appear on will be bulk loaded, possibly by someone else, at a later date. I would rather still have the database enforce the non-nullability of these fields. In the field templates I've tried moving the built-in SetUpValidator() call for the RequiredFieldValidator not to run when these specific fields are being loaded, and I've also tried disabling the RequiredFieldValidators and forcing their IsValid property to true. None of these actions allows me to submit the page.
Is there a way to tell EF/Dynamic Data to skip the validation for some fields?
EDIT
As noted below, I also tried marking them nullable in the model and not in the database, which caused an error: Problem in mapping fragments...Non-nullable column...in table...is mapped to a nullable entity property.
EDIT #2
I have found a solution that works, but requires modifying the auto-generated designer file for the entity set, which is fragile at best. I would love to know a "righter" way to do it, but if nothing becomes apparent in the next couple of days I'll post my own answer.
So here are the edits I found I had to make. When allowing the tool to create the entities in the edmx Designer.cs file I get properties like these:
for a datetime on the server side
[EdmScalarPropertyAttribute(EntityKeyProperty=false, IsNullable=false)]
[DataMemberAttribute()]
public global::System.DateTime CreatedDate
{
get
{
return _CreatedDate;
}
set
{
OnCreatedDateChanging(value);
ReportPropertyChanging("CreatedDate");
_CreatedDate = StructuralObject.SetValidValue(value);
ReportPropertyChanged("CreatedDate");
OnCreatedDateChanged();
}
}
for a varchar
[EdmScalarPropertyAttribute(EntityKeyProperty=false, IsNullable=false)]
[DataMemberAttribute()]
public global::System.String CreatedBy
{
get
{
return _CreatedBy;
}
set
{
OnCreatedByChanging(value);
ReportPropertyChanging("CreatedBy");
_CreatedBy = StructuralObject.SetValidValue(value, false);
ReportPropertyChanged("CreatedBy");
OnCreatedByChanged();
}
}
To make it work without validation for a DateTime property setting the IsNullable parameter of the EdmScalarPropertyAttribute to true is sufficient to avoid the issue. For the String property you also have to change the 2nd parameter of the SetValidValue method call to "true."
All of this said, the only reason that I'm leaving this as it is is because I don't expect to have to regenerated the entities more than once or twice before we move to a different platform for this site. And in this case, merging the version in I have checked in to git with the version generated by the tool allows me to avoid most of the headaches,
Here is my meta information for a read-only auto generated date field. I don't get validation controls validating these fields. Hope this helps.
[ReadOnly(true)]
[DataType(DataType.Date)]
[Column(IsDbGenerated = true, UpdateCheck = UpdateCheck.Never, AutoSync = AutoSync.Never)]
[UIHint("DateTime")]
[Display(Name = "Modified", Order = 1000)]
[DisplayFormat(ApplyFormatInEditMode = true, DataFormatString = "{0:d}")]
public object DateModified { get; private set; }