I've used WCF RIA services with Entity Framework to build a simple application which can display and updates data about school courses. This was done by following the Microsoft tutorials. Now I would like to have a chart which shows a count for how many courses are on a key stage.
Example:
Key Stage 3 - 20 courses
Key Stage 4 - 32 courses
Key Stage 5 - 12 courses
Displayed on any form of chart. I have no problem binding data to the chart in XAML. My problem is that I do not know how to correct way of getting the data into that format. The generated CRUD methods are basic.
I have a few thoughts about possible ways, but don't know which is correct, they are:
Create a View in SQL server and map this to a separate Entity in the Entity Data Model. Generating new CRUD methods for this automatically.
Customise the read method in the existing DomainService using .Select() .Distinct() etc. Don't know this syntax very well labda expressions/LINQ??? what is it? Any good quickstarts on it?
Create a new class to store only the data required and create a read method for it. Tried this but didn't know how to make it work without a matching entity in the entity model.
Something I am not aware of.
I'm very new to this and struggling with the concepts so if there are useful blogs or documentation I've missed feel free to point me towards them. But I'm unsure of the terminology to use in my searches at the moment.
One way to is to build a model class. A model is a class that represents the data you wish to display. For example i might have a table with 10 fields but i only need to display 2. Create a model with these two properties and return that from your data layer.
you can use entity framework to pump data into a new class like so
Model Class:
public class Kitteh
{
public string Name { get; set; }
public int Age { get; set; }
}
Entity Query:
public Iqueryable<Kitteh> getKittehz
{
var result = from x in Data.TblCats
select new Kitteh
{
Name = x.Name,
Age = x.Age
}
return result;
}
If you are interested in the best practices approach to building silverlight applications I would suggest you research the MVVM pattern.
http://www.silverlight.net/learn/videos/silverlight-4-videos/mvvm-introduction/
http://www.silverlight.net/learn/tutorials/silverlight-4/using-the-mvvm-pattern-in-silverlight-applications/
I am attempting a similar piece of work.
I will tell you the approach I am going to use and maybe that can help you.
I am going to create a class in the silverlight project to describe the chartItem: It will have 2 string properties : Key and Value.
Then create a collection object...In your case, this could be a class that has one property of type Dictionary<string,string> myCollection... or ObservableCollection<ChartItem> myCollection
The next step is to do a ForEach loop on the data coming back from the server and Add to your Collection.
myCollection.Add(new chartItem{ Key= "Key Stage 3", Value = "20 Courses" });
myCollection.Add(new chartItem{ Key= "Key Stage 4", Value = "60 Courses" });
myCollection.Add(new chartItem{ Key= "Key Stage 5", Value = "10 Courses" });
... more to follow if you are still looking for an answer
There is no easy way to include Views in Entity Framework as it does not allow any table/view to be included without "Key" (PrimaryKey) which will cause more efforts as you will have to map view manually in EDMX and then map keys etc.
Now we have found out an alternative approach,
Create View called ChartItems in your DB
Create LinqToSQL file ViewDB
Drag View ChartItems in ViewDB
Create ChartItem[] GetChartItems method in your RIA Domain Service Class as follow
public ChartItem[] GetChartItems(..parameters...){
ViewDB db = new ViewDB();
return db.ChartItems.Where(...query mapping...).ToArray();
}
RIA Domain Service Class can contain any arbitrary method that you can directly invoke from client with parameters. It is as simple as calling a web service. And you have to return an array because IQueryable may or may not work in some cases, but we prefer Array. You can try IQueryable but it may not work correctly against linq to SQL.
Related
I have an Open JPA entity and it successfully connects a many-to-many relationship. Right now I successfully get the entire table, but I really only want the ID's from that tables. I plan on calling the database later to reconstruct the entities that I need (according to the flow of my program).
I need only the ID's (or one column from that table).
1) Should I try and restrict this in my entity beans, or in the stateless session beans that I will be using to call the entity beans
2) If I try and do this using JPA, how can I specify that I only get back the ID's from the table, instead of the whole table? So far looking online, I don't see a way that you can do this. So I am guessing there is no way to do this.
3) If I simply just manipulate the return values, should I create a separate class that I will be returning to the user that will return only the required id list to the user?
I could be completely wrong here, but from the looks of it, I don't think there is a simple way to do this using JPA and I will have to return a custom object instead of the entity bean to the user (this custom object would only hold the id's as opposed to the whole table as it currently does)
Any thoughts... I don't think this is really relevant, but people are always asking for code, so here you go...
#ManyToMany(fetch=FetchType.EAGER)
#JoinTable(name="QUICK_LAUNCH_DISTLIST",
joinColumns=#JoinColumn(name="QUICK_LAUNCH_ID"),
inverseJoinColumns=#JoinColumn(name="LIST_ID"))
private List<DistributionList> distributionlistList;
Currently how I get the entire collection of records. Remember I only want the id...
try
{
//int daSize = 0;
//System.out.println("Testing 1.2..3...! ");
qlList = emf.createNamedQuery("getQuickLaunch").getResultList();
}
This is how I call the Entity beans. I am thinking this is where I will have to programatically go through and create a custom object similar to the entity bean (but it just has the ID's and not the whole table, and attempt to put the id's in there somewhere.
What are your thoughts?
Thanks
I believe I just figured out the best solution to this problem.
This link would be the answer:
my other stack overflow answer post
But for the sake of those too lazy to click on the link I essentially used the #ElementCollection attribute...
#ElementCollection(fetch=FetchType.EAGER)
#CollectionTable(name="QUICK_LAUNCH_DISTLIST",joinColumns=#JoinColumn(name="QUICK_LAUNCH_ID"))
#Column(name="LIST_ID")
private List<Long> distListIDs;
That did it.
Sounds like you want something like this in your quickLaunch class:
#Transient
public List<Integer> getDistributionListIds () {
List<Integer> distributionListIds = new LinkedList<Integer>();
List<DistributionList> distributionlistList = getDistributionlistList();
if (distributionlistList != null) {
for (DistributionList distributionList : distributionlistList)
distributionListIds.add(distributionList.getId());
}
return distributionListIds;
}
I had to guess a little at the names of your getters/setters and the type of DistributionList's ID. But basically, JPA is already nicely handling all of the relationships for you, so just take the values you want from the related objects.
One of my entity classes would be possible to store in a sql server
database as a BIGINT. My question is: How do I get a Entity Framework
context to know how to store and retrieve instances of my entity class?
More detail. I'm using Noda Time, which can represent a (much) wider range of
dates than can SQL or .NET datetime (AND it's a dessert topping). My Entity Class, Happening, is a wrapper around NodaTime's
Instant class. I can set a Happening from a long, and get a long from
a happening with methods like .SetFromLong(long instant) and .ToLong().
Currently I have my model working, saving classes that contain
properties of the dot net DateTime type. If instead I want to use properties
of my custom type "Happening", how do I tell Entity Framework how to save those?
If I'm reading this article about Modeling and Mapping am I on the
right track or missing something simpler?
http://msdn.microsoft.com/en-us/library/bb896343.aspx
I'm using entity framework 4.
What i recommend doing is adding 2 properties on your entity a NodaTime and a long, and exclude your NodaTime property using [NotMapped] in your EF model, then in your getter/setter update the long.
ie
public class MyEntity{
public long TimeAsLong{get;set;}
[NotMapped]
public Happening {
get{
return new Happening().SetFromLong(TimeAsLong);
}
set {
TimeAsLong = value.ToLong();
}
}
}
The effect of this will be that the long is stored in the db but you can access it on the class via NodaTime
I'm pretty new to the Entity framework and I'm modelling this simple structure:
With this model what I have is a Users class with a property UsersGroups (a collection of UserGroups objects).
I would like to have a Users class with a property like Groups with type Tuple or something like this (a new PriorizedGroup class, etc) that is much more related with the bussines.
Is this possible with the Entity framework?
Thanks in advance.
EDIT: If I were modeling the bussines objects I would create a User class with a Groups property that contained all the groups the user pertains with an extra property to store its priority (with a tuple, with an inherited class, as you wish). The thing is that I feel that the objects created by the Entity framework resemble the SQL structure, not the business structure.
Not directly. EF can map the relation only in the way you see it at the moment but you can add your custom behavior to your partial part of the entity. The simple way is something like
public partial class Users
{
public IEnumerable<PrioritizedGroup> Groups
{
get
{
return UserGroups.Select(ug => new PrioritizedGroup
{
Priority = ug.Priority,
Id = ug.Group.Id,
Name = ug.Group.Name,
Description = ug.Group.Description
})
.OrderBy(g => g.Priority);
}
}
}
To make this happen directly in EF you need some advanced mapping technique which will require you to modify EDMX source code directly (either DefiningQuery or QueryView) and it will make the entity read only (you will need stored procedures for modification).
To make the collection exposed on Users updatable you would probably need to use ObservableCollection and transfer all modifications triggered by ObservableCollection back to original UserGroups collection. Once you have something like that implemented you can hide original collection.
I'm using VS1010RC with the POCO self tracking T4 templates.
In my WCF update service method I am using something similar to the following:
using (var context = new MyContext())
{
context.MyObjects.ApplyChanges(myObject);
context.SaveChanges();
}
This works fine until I set ConcurrencyMode=Fixed on the entity and then I get an exception. It appears as if the context does not know about the previous values as the SQL statement is using the changed entities value in the WHERE clause.
What is the correct approach when using ConcurrencyMode=Fixed?
The previous values need to be in your object.
Let's say you have a property ConcurrencyToken:
public class MyObject
{
public Guid Id { get; set; }
// stuff
public byte[] ConcurrencyToken { get; set; }
}
Now you can set ConcurrencyMode.Fixed on that property. You also need to configure your DB to automatically update it.
When you query the DB, it will have some value:
var mo = Context.MyObjects.First();
Assert.IsNotNull(mo.ConcurrencyToken);
Now you can detach or serialize the object, but you need to include ConcurrencyToken. So if you're putting the object data on a web form, you'll need to serialize ConcurrencyToken to a string and put it in a hidden input.
When you ApplyChanges, you need to include the ConcurrencyToken:
Assert.IsNotNull(myObject.ConcurrencyToken);
using (var context = new MyContext())
{
context.MyObjects.ApplyChanges(myObject);
context.SaveChanges();
}
Having ConcurrencyMode.Fixed changes the UPDATE SQL. Normally it looks like:
UPDATE [dbo].[MyObject]
SET --stuff
WHERE [Id] = #0
With ConcurrencyMode.Fixed it looks like:
UPDATE [dbo].[MyObject]
SET --stuff
WHERE [Id] = #0 AND [ConcurrencyToken] = #1
...so if someone has updated the row between the time you read the original concurrency token and the time you saved, the UPDATE will affect 0 rows instead of 1. The EF throws a concurrency error in this case.
Therefore, if any of this isn't working for you, the first step is to use SQL Profiler to look at the generated UPDATE.
Mark,
The objects created as "Self-tracking entities" cannot be considered pure POCOs;
Here's the reason:
The STEs only work well if your client uses the generated proxies from the STE T4 template.
Change-tracking, and thus your service, will only work with these generated proxies.
In a pure POCO world (interoperatibility, Not all .Net 4.0 clients, .. ), you cannot put
constraints on you client. For instance, facebook will not be writing a service that can
only handle .Net 4.0 clients.
STEs may be a good choice in some environments, it all depends on your requirements.
I have a project where the client is using Entity Framework, and I'm trying to abstract away the generated classes from the rest of the application.
One generated class is Category and it has say Type as a property.
I've created an interface that I want Category to implement, like this:
public interface ICategory
{
string Type { get; set;}
}
I have done this in LINQ to SQL before and it works fine. I create a partial class in a separate file and have it implement the interface:
public partial class Category: ICategory
//implement interface
However, with EF whenever I try to build a query with EF it says it doesn't support OfType<>().
Example:
var query = from c in DataContext.Category
where Type == "some type"
select c;
var resultsList = query.OfType<ICategory>(); //error here (not supported)
What am I doing wrong here?
Other things to note: I'm developing this in a silverlight application and the data context is actually being pulled from a service, so there's a client server relationship going on here as well.
As a general rule, LINQ to Entities can only understand things which are part of your entity model (EDMX). So while you are free to extend your entity types be a partial classes, you cannot use properties, methods, and interface references you add there in LINQ to Entities queries, except for certain, very specific features.
However, in this case the following query should give you the result you want:
var resultsList = query.Select<ICategory>(c => c);