I have a list of tables and I'd like to select only necessary columns. How can I set filter witn FetchPolymorphic method?
FetchPolymorphic is done against an entity object when using SelfServicing so basically you are getting back an entity
C#
FamilyCarEntity car = (FamilyCarEntity)CompanyCarEntity.FetchPolymorphic(null, 4, null);
VB.NET
Dim car As FamilyCarEntity = CType(CompanyCarEntity.FetchPolymorphic(Nothing, 4, Nothing), FamilyCarEntity)
Once you have the entity object back (table or view) you can access it's properties (fields)
Using the Adapter is similar
Related
I am new to entity framework. I have a simple stored procedure that returns 2 result set.
I am using a code-first approach and need to merge the 2 result set into one single collection using "merge". I don't want to modify my stored procedure.
Any help would be appreciated. Thank you.
Just follow the doc here:
Entity Framework Sprocs with Multiple Result Sets
Except in your case both DataReaders load the same entity.
eg
var foos1= ((IObjectContextAdapter)db)
.ObjectContext
.Translate<Foo>(reader, "Foos", MergeOption.AppendOnly);
// Move to second result set and read next set of entities
reader.NextResult();
var foos2 = ((IObjectContextAdapter)db)
.ObjectContext
.Translate<Foo>(reader, "Foos", MergeOption.AppendOnly);
var foos = foos1.Union(foos2).ToList();
I am using Entity Framework 4.
I am trying to associate a new entity with an existing entity. The system ends up creating a new child entity when in fact I just want to add a reference to the child object to the parent.
There is a many to many relationship between the two entities so I cannot simply set the FK property of the parent entity. I have tried parent.ChildCollection.Add(child) which simply creates a new child object in the database. This is what I am trying to avoid.
I must be doing something obviously wrong.
thanks
updated code sample
Code sample for my Self-Tracking-Entities that I have to do client side
Right now I have something like this to get all children from server then loop through to find the one i want, then add it to the object collection
List<Service.Child> childs = _client.GetChildren();
I have to loop through that collection to find the right one to add to the parent.childs collection ie.
List<Service.Child> childList = new List<Service.Child>();
foreach (Service.Child child in childList) {
if (child.ChildId == childId)
childList.Add(child);
}
contact.Childs = childList;
If an entity originally came from the database and has its own EntityKey properties populated, using Add to link it to another entity will change its EntityState to Added. Even though it is a preexisting entity, SaveChanges will create an insert command for this entity. You should consider using Attach instead:
parent.ChildCollection.Attach(child);
Using the Attach method, you can define relationships between entities that already
exist in the ObjectContext but that have not been connected automatically.
I'm wondering if this is feasible and how. I've an entity that is a simple 1 to 1 mapping against a database. I'd like to add a custom property to this entity that is the result of a stored procedure call. This SP returns a collection of the same entity (hierarchical data).
Any ideas?
Thanks in advance,
Fabian
You could create a partial class with the same name and create a property that gets the collection. In the class have a private collection that you fill if empty in the get with a private function or just return it if the collection is already populated.
I'm trying to get to grips with EF this week and I'm going ok so far but I've just hit my first major snag. I have a table of items and a table of categories. Each item can be 'tagged' with many categories so I created a link table. Two columns, one the primary ID of the item, the other the primary ID of the category. I added some data manually to the DB and I can query it all fine through EF in my code.
Now I want to 'tag' a new item with one of the existing categories. I have the category ID to add and the ID of the Item. I load both as entities using linq and then try the following.
int categoryToAddId = Convert.ToInt32(ddlCategoriesRemaining.SelectedValue);
var categoryToAdd = db.CollectionCategorySet.First(x => x.ID == categoryToAddId);
currentCollectionItem.Categories.Add(categoryToAdd);
db.SaveChanges();
But I get "Unable to update the EntitySet 'collectionItemCategories' because it has a DefiningQuery and no element exists in the element to support the current operation."
Have I missed something? Is this not the right way to do it? I try the same thing for removing and no luck there either.
I think I have managed to answer this one myself. After alot of digging around it turns out that the Entity Framework (as it comes in VS2008 SP1) doesn't actually support many to many relationships very well. The framework does create a list of objects from another object through the relationship which is very nice but when it comes to adding and removing the relationships this can't be done very easily. You need to write your own stored procedures to do this and then register them with Entity Framework using the Function Import route.
There is also a further problem with this route in that function imports that don't return anything such as adding a many to many relationship don't get added to the object context. So when your writing code you can't just use them as you would expect.
For now I'm going to simply stick to executing these procedures in the old fashioned way using executenonquery(). Apparently better support for this is supposed to arrive in VS2010.
If anyone feels I have got my facts wrong please feel free to put me right.
After you have created your Item object, you need to set the Item object to the Category object on the Item's Categories property. If you are adding a new Item object, do something like this:
Using (YourContext ctx = new YourContext())
{
//Create new Item object
Item oItem = new Item();
//Generate new Guid for Item object (sample)
oItem.ID = new Guid();
//Assign a new Title for Item object (sample)
oItem.Title = "Some Title";
//Get the CategoryID to apply to the new Item from a DropDownList
int categoryToAddId = Convert.ToInt32(ddlCategoriesRemaining.SelectedValue);
//Instantiate a Category object where Category equals categoryToAddId
var oCategory = db.CategorySet.First(x => x.ID == categoryToAddId);
//Set Item object's Categories property to the Category object
oItem.Categories = oCategory;
//Add new Item object to db context for saving
ctx.AddtoItemSet(oItem);
//Save to Database
ctx.SaveChanges();
}
Have you put foreign keys on both columns in your link table to the item and the category or defined the relationship as many to many in the Mapping Details?
I've created a function import that returns the results of a stored proceedure as one of my entities. however I can't seem to traverse my through navigation properties to access the data in other entities. I know that you can use include() for objectQueries but can't find anything that will force the EF to load my relations for entity results of function imports.
Any ideas??
Thanks in advance.
This is not possible in EF 1.0
The reason is that EF will consider stored procedure values to be just values and not navigation properites.
For example, Employee entity has multiple Order entities. In Order you have a property called EmployeeID. When the database fills your query using include statements, it creates 1 projection query in SQL to populate all of the Order data that a particular Employee could have.
So if I said
var employee = context.Employees.Include("Orders").Where(e => e.ID == 1).First();
var orders = employee.Orders;
The SQL for the first query will create a projection query which will contain orders where the EmployeeID = 1.
Now when your stored procedure runs, this can do any code behind the scenes (in otherwords it can return any set of data). So when SQL runs the stored procedure, it just runs the code in that stored procedure and does not have any knowledge that EmployeeID on Order is an FK to that property. Additionally, if your stored procedure returns an Employee entity, then you are looking at another scenario where you will not even have an OrderID to pursue.
To work around this though, you can setup your query in EF using Include statements that can mirror any stored procedure. If you use the proper mix of .Select and .Include statements you should be able to do the same thing.