To simplify my current situation lets say I have 2 tables (legacy so can't touch the schema to play better with Linq)
node
Columns: key_field1, key_field2, [lots of other fields]
node_children
Columns: parent_key_field1, parent_key_field2, child_key_field1, child_key_field2
node_children is similar to the has_and_belongs_to_many join table from Rails... except that both ids refer to the same table.
Ideally I would like to have a Node Class which has a Property Children, which returns the right List?
Results should be equivalent to
select * from node
join node_children
on node.key_field1 = node_children.child_key_field1 and node.key_field2 = node_children.child_key_field2
where node_children.parent_key_field1 = #paramX and node_children.parent_key_field2 = #paramY
Whats the best way to model this in Linq to Sql?
This is what I came up with (works too!)
Open up the ORM generated Node class MyDatabase.cs
partial class Node
{
public IEnumerable<Node> Children
{
get
{
MyDatabaseDataContext dc = new MyDatabaseDataContext();
return from link in this.ChildLinks
join node in dc.Nodes on new { Site = link.child_key_field1, ID = link.child_key_field2 } equals new { Site = node.key_field1, ID = node.key_field2 }
select node;
}
}
}
The ORM designer automatically adds an association between the two tables. I renamed the property on the Node class to ChildLinks.
(This drove me up the wall for a couple of hours) For the LINQ join to work with composite keys, you need the Name as well as Order of each part to match. See How to: Join by Using Composite Keys
One of these days, I'm gonna complete the LINQ Getting Started set of articles :)
Related
I want to write a simple query to retrieve a list of USER with a simple restriction on CUSTOMER joined table.
I'm only interested by the USER entity.
If I write it using HPQL :
public List<Users> getAssociatedAdminObs(Integer pCustId) {
Criteria crit = getCriteriaForObsAdmin("USER");
crit.createCriteria("clients").add(Restrictions.eq("idCustomer", pCustId));
return crit.list();
StringBuilder hqlQuery = new StringBuilder().append("select u from Users as u join u.customers as c where c.idCustomer=:idCustomer");
Query q = getSessionAndManageFilter().createQuery(hqlQuery.toString());
q.setInteger("idCustomer", pCustId);
return q.list();
}
The SQL generated only Select all the fields from USER entity, as expected.
Now if I write it through Hibernate criteria API :
public List<Users> getAssociatedAdminObs(Integer pCustId) {
Criteria crit = getSession().createCriteria(Users.class);
crit.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
crit.createCriteria("customers").add(Restrictions.eq("idCustomer", pCustId));
return crit.list();
}
The SQL generated Select all the fields from USER entity but also from the CUSTOMER entity.
I'm using hibernate-core 3.3.1.GA.
I know I can use projection to work around the issue but my object will be transient, I also validated it works using a subquery to do my restrictions.
But I'm not happy with using workarounds and I do not understand why it would behave differently between the 2 code examples ?
It doesn't make sense to me to select fields outside of the asked entity.
Let's say I have a Company table and a Division table. Each Division has a Foreign key to a company so each company can have many Division children.
If I grab a Company object with Linq-to-sql I have a access to it's Divisions property, a entity set of Division objects. If I add a new Division object to it and call SubmitChanges() won't it automatically go into the Division table or am I forced to call InsertOnSubmit?
There are multiple ways to insert objects into the database with LINQ to SQL. For instance:
db.Divisions.InsertOnSubmit(new Division()
{
Company = db.Company.Single(c => c.Id == 1),
// other properties
});
db.SubmitChanges();
Or:
var company = db.Company.Single(c => c.Id == 1);
company.Divisions.Add(new Division()
{
// other properties
});
db.SubmitChanges();
As you can see, you can use the InsertOnSubmit of the Table<Division> Divisions property on the data context, but you can also use the Add method of the EntitySet<Division> Divisions property on the Company entity. They both do -about- the same. Nice about the latter approach is that you don't need to 'link' the company to the new division, because LINQ to SQL can figure that out for you.
I hope this answers your question.
I am implementing the asp.net MVC web application, where i am using the Linq to Sql to manipulate the data in database. but in my one of action, i want to insert multiple table entries which are depends upon each other by referring previous insertion Id's. So i just wnat to know how to handle the transaction, like begin transaction, commit,rollback and all like in ADO.net. how to manage this. what if one of insertion get crashed in the middle of manipulation?
Note:- I am not using the Stored procedures here. I am using Lambda expressions and methods. Also these are use in different manager classes.
Example:
For Create Subject - used method in SubjectManager class to insert subject infor, that returns subject Id. within this subjectid i am inserting the let say its chapters with another method in manager class as ChapterManager. which again returns the ChapterId, on base of this chapeter Id , inserting the Topics of chapter. that again uses Topic manager same like above.in each manger class i am creating dataContext object for the same. and I am controlling all this within a single action in my controller. but worrying about the transaction management. how I can use here ?
The DataContext already includes an embedded transaction object. For example, let's say you are placing a new order for a customer. You can set up your model so that the following code updates both the Customer AND Order table with a single SubmitChanges. As long as a foreign key relationship exists between the two tables, the embedded transaction object handles both the Customer update and the Order insert in the same transaction. Using a TransactionScope object to encase a single DataContext is redundant:
using (DataContext dc = new DataContext())
{
Order order = new Order();
order.ProductID = 283564;
order.Quantity = 7;
order.OrderDate = DateTime.Now;
Customer customer = dc.Customers.Single(c => c.CustomerID == 6);
customer.LastUpdate = order.OrderDate;
customer.Orders.Add(order);
dc.SubmitChanges();
}
using(TransactionScope scope = new TransactionScope())
{
using(DataContext ctx = new MyDataContext())
{
ctx.Subject.Add(subject);
Chapter chapter = new Chapter();
chapter.SubjectId = subject.Id;
ctx.SubmitChanges();
ctx.Chapter.Add(chapter);
ctx.SubmitChanges();
scope.Complete() // if it all worked out
}
}
From the System.Transactions namespace I believe.
I am hoping you can help. I am developing a tiered website using Linq to Sql. I created a new class(or object) in DBML designer called memberState. This object is not an actual table in the database. I have this method in my middle layer:
public override IEnumerable(memberState) GetMembersByState(string #state)
{
using (BulletinWizardDataContext context = DataContext)
{
IEnumerable(memberState) mems = (from m in context.Members
join ma in context.MemberAddresses
on m.UserId equals ma.UserId
join s in context.States
on ma.StateId equals s.StateId
where s.StateName == #state
select new memberState
{
userId = m.UserID,
firstName = m.FirstName,
middleInitial = m.MiddleInitial,
lastName = m.LastName,
createDate = m.CreateDate,
modifyDate = m.ModifyDate
}).ToArray(memberState)();
return mems;
}
}
The tables in my joins (Members, States, and MemberAddresses are actual tables in my Database). I created the object memberStates so I could use it in the query above (notice the Select New memberState. When the data is updated on the web page how do I persist the changes back to the Member Table? My Member Table consists of the following columns: UserId, FirstName, MiddleInitial, LastName, CreateDate, ModifyDate. I am not sure how save the changes back to the database.
Thanks,
If I remember correctly, you can create a view from the different tables (Members, States, and MemberAddresses) and add that to the data context. Then any modifications to data in the view object can be saved, and linq to sql will handle the commit correctly as long as all the relationships are clearly setup/defined in both the database and in the data context.
If you have a Member table, the dbml will most likely contain a Member class. To update a member in the database, you will have to create a new Member object, and the Attach it to the BulletinWizardDataContext.Members collection. Something similar to the following code should the trick (I have not tested the code):
using (BulletinWizardDataContext context = DataContext)
{
Member m = new Member() { UserId = userId };
context.Members.Attach(m);
m.FirstName = firstName;
// Set other properties
context.SubmitChanges();
}
Attach must be called before setting the properties. Also, Linq2Sql has some issues with Attach in the case where the properties of your object are set to default values (i.e. 0 for numeric values, false for booleans, null for string etc.). In this case Attach will not generate the correct SQL.
var m = myContext.Members.Single(m=> m.UserID == myMemState.userID);
m.FirstName = myMemState.firstName;
m.MiddleInitial = myMemState.middleInitial;
...
That would be the quick way. It does an additional roundtrip to the db, but will work well. If that's an issue for you, then do Attach like Jakob suggested. For that you have to have to do some extra steps, like reviewing the configuration for optimistic updates and make sure you have the original fields when doing the attach.
We have followed the approach below to get the data from multiple results using LINQ To SQL
CREATE PROCEDURE dbo.GetPostByID
(
#PostID int
)
AS
SELECT *
FROM Posts AS p
WHERE p.PostID = #PostID
SELECT c.*
FROM Categories AS c
JOIN PostCategories AS pc
ON (pc.CategoryID = c.CategoryID)
WHERE pc.PostID = #PostID
The calling method in the class the inherits from DataContext should look like:
[Database(Name = "Blog")]
public class BlogContext : DataContext
{
...
[Function(Name = "dbo.GetPostByID")]
[ResultType(typeof(Post))]
[ResultType(typeof(Category))]
public IMultipleResults GetPostByID(int postID)
{
IExecuteResult result =
this.ExecuteMethodCall(this,
((MethodInfo)(MethodInfo.GetCurrentMethod())),
postID);
return (IMultipleResults)(result.ReturnValue);
}
}
Notice that the method is decorated not only with the Function attribute that maps to the stored procedure name, but also with the ReturnType attributes with the types of the result sets that the stored procedure returns. Additionally, the method returns an untyped interface of IMultipleResults:
public interface IMultipleResults : IFunctionResult, IDisposable
{
IEnumerable<TElement> GetResult<TElement>();
}
so the program can use this interface in order to retrieve the results:
BlogContext ctx = new BlogContext(...);
IMultipleResults results = ctx.GetPostByID(...);
IEnumerable<Post> posts = results.GetResult<Post>();
IEnumerable<Category> categories = results.GetResult<Category>();
In the above stored procedures we had two select queries
1. Select query without join
2. Select query with Join
But in the above second select query the data which is displayed is from one of the table i.e. from Categories table. But we have used join and want to display the data table with the results from both the tables i.e. from Categories as well as PostCategories.
Please if anybody can let me know how to achieve this using LINQ to SQL
What is the performance trade-off if we use the above approach vis-à-vis implement the above approach with simple SQL
Scott Guthrie (the guy who runs the .Net dev teams at MS) covered how to do this on his blog some months ago much better than I ever could, link here. On that page there is a section titled "Handling Multiple Result Shapes from SPROCs". That explains how to handle multiple results from stored procs of different shapes (or the same shape).
I highly recommend subscribing to his RSS feed. He is pretty much THE authoritative source on all things .Net.
Heya dude - does this work?
IEnumerable<Post> posts;
IEnumerable<Category> categories;
using (BlogContext ctx = new BlogContext(...))
{
ctx.DeferredLoadingEnabled = false; // THIS IS IMPORTANT.
IMultipleResults results = ctx.GetPostByID(...);
posts = results.GetResult<Post>().ToList();
categories = results.GetResult<Category>().ToList();
}
// Now we need to associate each category to the post.
// ASSUMPTION: Each post has only one category (1-1 mapping).
if (posts != null)
{
foreach(var post in posts)
{
int postId = post.PostId;
post.Category = categories
.Where(p => p.PostId == postId)
.SingleOrDefault();
}
}
Ok. lets break this down.
First up, a nice connection inside a using block (so it's disposed of nicely).
Next, we make sure DEFERRED LOADING is off. Otherwise, when u try and do the set (eg. post.Category == blah) it will see that it's null, lazy-load the data (eg. do a rountrip the database) set the data and THEN override the what was just dragged down from the db, with the result of there Where(..) method. phew! Summary: make sure deferred loading is off for the scope of the query.
Last, for each post, iterate and set the category from the second list.
does that help?
EDIT
Fixed it so that it doesn't throw an enumeration error by calling the ToList() methods.
Just curious, if a Post have have one or many Categories, is it possible to instead of using the for loop, to load the Post.PostCategories with the list of Categories (one to many), all in one shot, using a JOIN?
var rslt = from p in results.GetResult<Post>()
join c in results.GetResult<Category>() on p.PostId = c.PostID
...
p.Categories.Add(c)