ADO.NET :: Entity Framework - Query Based On Relationships?
Oct 27, 2010
I have the following related tables:
Users
Id
Username
Email
Password
UserStatuses
Id
Name
Users_UserStatus
Id
User (FK - Users: Id)
Status (FK - UserStatuses: Id)
StatusDate
As you can see, UserStatuses is a reference table with various statuses. Users_UserStatus is a join table between Users and UserStatuses. Using Entity Framework, how can I do a conditional to check if the latest StatusDate is "Pending"? As of now, I have the following:
[Code]....
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Jan 19, 2011
I would like to have a short example on how do you actually perform relationships in Entity Framework 4 Code-First CTP 5 ?
Would love an example for these kind of relations :
* one-to-many
* many-to-many
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May 29, 2010
I need to check if any rows are returned in a QueryString here's what I have so far.not sure what code to put to see if the row count is greater than 1
private void BindDataToGrid()
{
//MessageBoardEntities3 is ThemeableAttribute connection string name
int TID = Convert.ToInt32(Request.QueryString["ThreadID"].ToString()); // if Post ID is int
var context = new MessageBoardEntities3();
gvPosts.DataSource = from p in context.Posts
where p.ThreadID == TID
select new { p.Post1, p.PostID };
gvPosts.DataBind();
lblNoPosts.Text = "No posts found for this thread.";
}
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Feb 4, 2010
I am just getting started with entity framework with asp.net 3.5 using VS 2008
There are two tables, Categories & Subcategories:
Category table: CID, CategoryName Sub Category table: SID, CID, SubCategoryName I would like to get SID, CID, CategoryName, SubCategoryName in the gridview. Just as we write a select statement i.eSelect a.sid, b.cid, b.categoryname, b.subcategoryname from subcategories a inner join categories b on a.cid=b.cid & put the same in a gridview.
I was trying for the whole day & couldnt get atleast one url that would teach how to do it.
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Jun 11, 2010
There are some tutorials explaining how to create a Model based on Linq to Sql or The Ms Entity Framework. Can I use my custom code for a model? If we have the controller with the code :
[Code]....
This returns a List<Movie> to the view that knows what to do with it. Is it possible that I create a method called MovieSet that returns a List<Movie> using a sql qry or a stored procedure call without the creation of an Object for this purpose ? Or do I need a Movie object? Lets say that I just to do my query, loading data into a dataTable and load that data to a list of movie objects. Because the code created by the Entity Framerwork is too big for a quick reading.
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May 19, 2010
I am using MUSQL Database extensivly in my projects,
can we build ADO.NET entity framework based on MYSQL database?
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Oct 13, 2010
Best way to show the SQL trace of a LINQ query to Entity Framework 3.5? I am using ASP.net and EF 3.5.
Dim dbo As Web.Portal.RBMEntities = New Web.Portal.RBMEntities
Dim Query = From RoleAllocations In dbo.RoleAllocations Where RoleAllocations.user_id = _ID And RoleAllocations.expire_date > Today Select RoleAllocations
Console write the SQL trace?
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Nov 29, 2010
I have a strange error, I've tried to search for it before writing this post but I wasn't able to find out a solution yet.
I'm executing a query using ExecuteStoreQuery against a MySQL database, but it throws an exception reporting that there's a syntax error in my SQL.
I've tried to copy&paste the sql query into the MySQL tool and it works nicely, giving the correct results.
I've tried to open manually the connection and using CreateCommand to use it the "old way".
My query is a bit long, 4000 chars more or less, could it be the problem?
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Jan 22, 2011
I have a web app for our golf club. When I compute handicap index for each golfer, I have to select the most recent scores and then a subset of those scores depending on how many rounds of golf the golfer has played. All the scores are entered into a single SQL Express table called "Rounds". Verbally, this is what I'm trying to do:
1) select the twenty most recent golf scores (sort on date descending, "take(20)") [if less than 20 records, then select all available];
2) for this set of records, select the 10 lowest scores (or smaller number if golfer has less than 20 rounds);
3) compute the average round differential for the subset of records, etc. to calculate handicap index (this step is working ok...)
My current VB code has this LINQ query (which is flawed -- it selects the lowest handicap differential scores of ALL records for the filtered user):
[Code]....
How do I modify this query to accomplish items 1) & 2) above? It seems this should be simple, but my experience with queries is still limited.
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Jan 3, 2011
I have the following classes:
public class Category
{
public int CategoryId { get; set; }
public string Name { get; set; }
}
public partial class CategoryMap : EntityTypeConfiguration<Category>
{
public CategoryMap()
{
this.HasKey(c => c.CategoryId);
this.Property(c => c.Name).IsRequired().HasMaxLength(400);
}
}
public class MyObjectContext : DbContext
{
public MyObjectContext(string connectionStringName)
: base(connectionStringName)
{
}
public DbSet<Category> Categories { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new CategoryMap());
base.OnModelCreating(modelBuilder);
}
}
Now when I run the following code I get an exception (GenericArguments[0], 'System.Int32', on 'System.Data.Entity.Internal.Linq.ReplacementDbQueryWrapper`1[TEntity]' violates the constraint of type 'TEntity')
DbDatabase.SetInitializer<MyObjectContext>(new DropCreateDatabaseIfModelChanges<MyObjectContext>());
using (var context = new MyObjectContext("NopSqlConnection"))
{
var query1 = from c in context.Categories
select c.CategoryId;
var test1 = query1.ToList(); //works fine
var query2 = from c in context.Categories
where query1.Contains(c.CategoryId)
orderby c.Name descending
select c;
var test2 = query2.ToList(); //throws the exception
}
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Sep 9, 2010
I am new to this, and I am trying to implement a linq query similar to db.Genres.Include("Albums") command from
mvc music store using my current DB setup. I realize that the tutorial mentions Checlking the "Include foreign key columns in the method" when creating the tables in ADO.NET, but if I am using LINQ to SQL classes, then how can I obtain the same effect. And how do I use
db.Genres.Include("Albums") to simplify my life?
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May 26, 2010
I just tring to a complex (for me) with ado.net entity framework this is the structure: In practice it is a sort of group purchasing (Buyers) For each group of purchase (Buyer) should have the opportunity 'to select all products of the brands indicated in buyer I'm doing function to return correct data like this:
public List<Product> GetProductsByBuyer(int vBuyerId)
{
Buyersctx.Products.MergeOption = MergeOption.NoTracking;
return (from lProduct in Buyersctx.Products.Include("Brand").Include("Buyers")
where select lProduct).ToList();
}
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Mar 26, 2011
I'm currently learning entity framework (from the Julia Lerman book "Programming Entity Framework") and got really confused at the grouping part.
var contacts = from c in context.Contacts
group c by c.Title into myGroup
select myGroup;
This is supposed to return a Grouping<K,T> type, but the book didn't give an example on how exactly do I access this "contacts" query and I can't figure it out. When I did foreach(var contact in contacts), my "contact' variable has no knowledge of any of the properties of the Contact type (contact.FirstName etc).
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Jun 28, 2012
I wrote a defining query
<EntitySet Name="EntityFramework" EntityType="SEOAnalysisModel.Store.EntityFramework">
<DefiningQuery>
SELECT Keyword, ResultHead ,Year from SeoAnalysis where Year = 2005
[Code].....
And this column value is repetative.
Now how can i get all column value?
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Oct 25, 2010
Is there a way to export a EF 4.0 Data Model to EF 3.5?
I looked around and found that we are not able to access EF 4.0 from a ASP.Net 3.5 project here: [URL]
Our project is the 1st to go to .Net 4.0 using Entity Framework and we (the team) were wondering if there was a way for the other projects that "might" need to access our data that are still using the .Net 3.5 framework.
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Apr 10, 2010
EF is so frustrating. I can't seem to be able to get my head around what I need to do so I can delete an object. I seem to be able to remove the object but not the related child objects. Can anyone tell me what is the rule of thumb when you want to delete all related child objects of a given object? I've tried loading all related objects like this:
Entry entry = ModelContext.GetObjectByKey(new EntityKey("ModelContainer.EntrySet", "Id", id)) as Entry;
entry.ChildEnteries.Load();
if (entry != null)
{
ModelContext.DeleteObject(entry);
ModelContext.SaveChanges();
}
I get errors related to the relationships: A relationship is being added or deleted from an AssociationSet 'EntryEntry'. With cardinality constraints, a corresponding 'Entry1' must also be added or deleted. Why can't I just load the object using modelcontext.GetObjectByKey and remove it along with its child objects? My other question is can I delete an object using Entity command like so? DELETE e from objectset as e where e.id = 1 I've tried few variations and all of them throw exceptions.
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Jan 24, 2011
I'm a newbie to this so bear with me. From what I've read online LINQ to Entity should see the relationships without having to specify the joins between multiple tables. I have a relationship that goes across 4 tables Employee, EmployeeDepartmentLink, EmployeeProjectLink, and Project. The idea is an employee can be in multiple departments and work on multiple projects with it being specified which department the employee is in for that project.
This is a C# MVC3 program connecting to a SQL database using VS 2010 Express.
I have no problem with running this query to find employees on a project:
[Code]....
Tring to do the reverse, finding projects that an employee worked on results in an error:
[Code]....
Error message: The specified type member 'EmployeeDepartmentLinks' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported. So I have 2 questions,
1) Why would it work in one direction and not the other? I've played around with it for a couple days with the same results.
2) Does it matter that my primary key and foreign keys are not named the same since all the relationships are connected in SQL? Ex: in Employee (EmployeePK)--(EmployeeFK) in EmployeeDepartmentLink Trying different stuff in LINQPad I was able to get the 2nd query to work if I specified all the joins which I thought was not neccesary with LINQ to Entity. I converted an SQL query that I made on the server into a LINQ query below which works.
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Nov 2, 2010
I am new to entity framework , it is really very good , but I want to know what is the difference between using entity framework with stored procedure or without stored procedure , which one the faster and what is the benefits for using stored procedures with entity framework.
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Jun 30, 2010
I have an EDM, it includes the entities extension and history. My goal is to use history to keep track of all the changes made to extension entity. For example, if extension with ID 223 has its property 'Name_Display' changed - I want the history entity to record this.
I'm using ASP.NET with VB.NET. Where in my code do I put the hook to say, "update the history entity" and what should that hook look like?
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Feb 9, 2011
I get an cast exception when i am trying to insert an entity in Entity Framework (using code-first). From this code :
public virtual T Insert(T entity)
{
return Context.Set<T>().Add(entity);
}
The cast exception is like "impossible to cast ...Collection'1(Entity) to type (Entity)" I can't figure out why. I am pretty sure ive done everything right. Post entity
public class Post
{
public long PostId { get; private set; }
public DateTime date { get; set; }
[Required]
public string Subject { get; set; }
public User User { get; set; }
public Category Category { get; set; }
[Required]
public string Body { get; set; }
public virtual ICollection<Tag> Tags { get; private set; }
public Post()
{
Category = new Category();
if (Tags == null)
Tags = new Collection<Tag>();
}................................
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Feb 10, 2011
I am mapping a stored procedure to an entity by right clicking on the entity (in the .edmx) and selecting "Stored Procedure Mapping." This brings you to a Mapping Details - "Name of Entity" Window that allows you to select the insert, update, and delete stored procedures associated with the Entity. It also maps the stored procedure parameter to the Entity "Property" (Column).
I'm gettin an error "error 2042: Parameter Mapping specified is not valid." The cause of the error is fairly obvious, in the Insert stored procedure that has been selected, a 'CHAR' parameter is being mapped to an Int32 Entity Property. I altered the stored procedure parameter to match the entity, I deleted the stored procedure, readded, and reslected it as the Insert function. I also cleaned, validated, updated model from database. No matter what I do, the parameter list in the mapping details doesn't reflect the change to the stored procedure. It's stuck on a char --> int32 mapping, even though it has been changed, like it's buried deep in meta data some where.
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Aug 5, 2010
I am trying to add a new entity and have to refernce associated data to add it. I cannot load the Referencetables. Giving "The EntityReference could not be loaded because it is not attached to an ObjectContext." How do i complete this task in Entity Framework 3.5
[Code]....
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Mar 31, 2011
I have a stupid problem with the Entity Framework. I get the following Exception:
[Code]....
I have an entity with a 4 fields representing the primary key. I copy it via serialization (works fine). I set the old entity to not valid (Datefield set to a date in the past, this field is part of the PK) and set the copied entity to DateTime.Now.Date. When I call context.AddObject I get the Exception above. I tried copying the entity via reflection but the entity has 3-4 references. And when copied, I get another Exception before even Adding the entity to the context. I also tried setting newObj.EntityKey = null and reset all the fields neccessary for the PK. I just want a whole copy of an entity with a different primary key (and some other fields changed too) and Create it in the database.
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Sep 21, 2010
I'm writing a custom .NET MembershipProvider (not the built in one) and trying to update using Entity Framework. But of course i have no access to (Try)UpdateModel. How can i update it?
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Jan 5, 2011
I have an Events table and an InstallmentPlans table. The relationship is 0..1 : an Event can have 0 or 1 Installment plans. If I want to remove the existing InstallmentPlan for an event, how do I do this? Setting it to null doesn't seem to work:
_event.InstallmentPlan = null;
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