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.
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.
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 new to linq to sql
I wrote this function:
public ICollection<ICustomer> GetAll()
{
DataClasses1DataContext context = new DataClasses1DataContext();
var customers = from customer in context.Customers select customer;
return customers.ToList().Cast<ICustomer>().ToList();
}
But it always return list of null values.
The database contain 3 records "filled with data" but this function return 3 nulls.
how to fix that?
It may not be able to cast the results properly, have you made your partial Customer object implement ICustomer? If not, that is the reason.
Also you don't have to bring it to a list twice, or even once for that matter since you aren't returning a list, it might be more appropriate to change your signature to List or IEnumerable depending on your usage.
You can test whether or not the cast is succeeding by doing a simple test.
DataClasses1DataContext context = new DataClasses1DataContext();
var customers = from customer in context.Customers select customer;
int numberOfCustomers = customers.Count();
var myCustomers = customers.Cast<ICustomer>(); //you could also do .OfType<ICustomer>();
int numberOfICustomers = myCustomers.Count();
If numberOfCustomers is 3 and numberOfICustomers is 0 then you know that was the issue.
Your problem is almost certainly at the .Cast() method (confirm this by stepping through your code & ensuring that customers is populated correctly).
Does the Customer object implement the ICustomer interface? It sounds like an obvious thing to check but that would be a likely problem.
I'm trying to copy all object attibutes to another object, fox example:
Person p1 = new Person();
p1.name = "John";
p1.sex = 'M';
Person p2 = new Person();
p2 = Util.Clone(p1);
The problem is that Person entity has an identity PK 'codPerson' and I don't want to copy this PK. Is there a way to clone/copy an object, but don't copy its PK attribute??
Thanks!!!
Perhaps you might consider the following:
Ensure Util.Clone(Person p) doesn't
copy the codPerson attribute
Clear the attribute after the Clone method
is called
Create a new Person object while specifically initializing specific properties.
At the most basic level you can't - given an arbitrary object o (and the question implies you're looking for generic solutions) you have no way to determine which field is a primary key.
So you step up a level - by adding some constraints i.e. that you will inform your tools what the primary key field is (or fields are) and hence enable use of a generic method.
So, you could explicitly specify the PK field (name) to the code that does the clone (I assume that you're using reflection to avoid explicitly copying all the fields). You could identify the PK by using annotation of some sort on the classes being cloned and have the clone code exclude properties with the relevant annotation (the annotation implies that the field won't be cloned). There may be other methods
You mention Linq - are you using a specific bit of Linq ?
Beyond that there's not a lot one can suggest without more details - ah but the question is tagged with Linq to SQL (which I missed) ok...
There's nothing obvious in a Linq to SQL class that will help - nor with the "table" but a quick look at the generated code in .designer.cs shows that a key field has annotations similar to the following (taken from a set of classes I have to hand):
[Column(Storage="_ID", AutoSync=AutoSync.OnInsert, DbType="Int NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)]
Therefore when you're do your reflection on the class to enumerate the properties to copy you'll want to look for the column and the "IsPrimaryKey" property within the column - unfortunately the details of how to do that are some distance outside my comfort zone!
You could manually set the properties on the new object to be equal to the old one.
For example:
Person p2 = new Person {
Name = p1.Name,
Gender = p1.Gender,
//...
};
you can use .net Reflection.
//using System.Reflection;
var yourEntity = new Person {Name = "Green", Surname= "White"};
var cloneEntity = new Person();
var allPi = typeof(Person).GetProperties();
foreach (var pi in allPi)
{
if (pi.Name != "codPerson" && pi != null && pi.CanWrite)
pi.SetValue(cloneEntity , pi.GetValue(yourEntity , null));
}
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)