I have a table Table1 has columns ID (int) and XMLTEXT of xml type
Can any one provide me LINQ query which is equivalent to below sql query
Update Table1 set XMLTEXT .modify('delete (/root/child1/child2)')
where ID=1001
In Linq2SQL, something like this should work.
long ProductID = 1;
ORM.Table1 p = context.Table1s.Where(o => o.ID == ProductID).FirstOrDefault();
if(p != null) {
p.XMLTEXTe.Element("child2").Remove();
// Need to do this so Linq picks up on the data change
// as it doesnt implement the correct XElement data changed event handler
// and thus won't submit the changes made if you dont do the reassignment!
p.XMLTEXT = new XElement(p.XMLTEXT);
context.SubmitChanges();
}
Related
i want to be able to do such a projection:
var result = from record in MyTable
select MapTo( record );
/*
select new RecordModel( )
{
RecordId = record.Id,
Property1 = record.Property1
};
*/
private RecordModel MapTo( MyTable dbRecord )
{
return new RecordModel( )
{
RecordId = dbRecord.Id,
Property1 = dbRecord.Property1
};
}
but i always get a 'NotSupportedException' (has no supported translation to sql).
I'm not sure if this is even possible but it would be nice^^
Maybe this is possible when i use an expression but i don't know how to code such an expression.
Linq tries to add the method to the query and sees it cannot be translated to Sql.
To be able to execute any CLR method in the Linq query, you need to execute the sql part of it first, so that you operate on in-memory objects. Like this:
var result = from record in MyTable.ToList()
select MapTo(record);
Anything that forces MyTable to enumerate its entries should work.
I have 2 tables that I need to load together all the time, the both must exist together in the database. However I am wondering why Linq to Sql demands that I have to load in a collection and then do a join, I only want to join 2 single tables where a record where paramid say = 5, example...
var data = _repo.All<TheData>(); //why do I need a collection/IQueryable like this?
var _workflow = _repo.All<WorkFlow>()
.Where(x => x.WFID== paramid)
.Join(data, x => x.ID, y => y.WFID, (x, y) => new
{
data = x,
workflow = y
});
I gues then I need to do a SingleOrDefault()? If the record is not null pass it back?
I Understand the Sql query comes out correctly, is there a better way to write this?
NOTE: I need to search a table called Participants to see if the loggedonuser can actually view this record, so I guess I should leave it as this? (this is main requirement)
var participant = _repo.All<Participants>();
.Any(x=> x.ParticipantID == loggedonuser.ID); //add this to above query...
The line var data = _repo.All<TheData>(); is something like saying 'start building query against the TheData table'.
This function returns you an IQueryable which will contain a definition of the query against your database.
So this doesn't mean you load the whole TheData table data with this line!
The query will be executed the moment you do something like .Count(), .Any(), First(), Single(), or ToList(). This is called deferred execution.
If you would end your query with SingleOrDefault() this will create a sql query that joins the two tables, add the filter and select the top most record or null(or throw an error if there are more!).
You could also use Linq instead of query extension methods.
It would look like:
var data = _repo.All<TheData>();
var _workflow = from w in _repo.All<WorkFlow>()
join t in _repo.All<TheData> on w.Id equals t.WFID
where x.WIFD = paramid
select new
{
data = t,
workflow = x
});
I am trying to get the records from the 'many' table of a one-to-many relationship and add them as a list to the relevant record from the 'one' table.
I am also trying to do this in a single database request.
Code derived from Linq to Sql - Populate JOIN result into a List almost achieves the intended result, but makes one database request per entry in the 'one' table which is unacceptable. That failing code is here:
var res = from variable in _dc.GetTable<VARIABLE>()
select new { x = variable, y = variable.VARIABLE_VALUEs };
However if I do a similar query but loop through all the results, then only a single database request is made. This code achieves all goals:
var res = from variable in _dc.GetTable<VARIABLE>()
select variable;
List<GDO.Variable> output = new List<GDO.Variable>();
foreach (var v2 in res)
{
List<GDO.VariableValue> values = new List<GDO.VariableValue>();
foreach (var vv in v2.VARIABLE_VALUEs)
{
values.Add(VariableValue.EntityToGDO(vv));
}
output.Add(EntityToGDO(v2));
output[output.Count - 1].VariableValues = values;
}
However the latter code is ugly as hell, and it really feels like something that should be do-able in a single linq query.
So, how can this be done in a single linq query that makes only a single database query?
In both cases the table is set to preload using the following code:
_dc = _db.CreateLinqDataContext();
var loadOptions = new DataLoadOptions();
loadOptions.LoadWith<VARIABLE>(v => v.VARIABLE_VALUEs);
_dc.LoadOptions = loadOptions;
I am using .NET 3.5, and the database back-end was generated using SqlMetal.
This link may help
http://msdn.microsoft.com/en-us/vcsharp/aa336746.aspx
Look under join operators. You'll probably have to change from using extension syntax other syntax too. Like this,
var = from obj in dc.Table
from obj2 in dc.Table2
where condition
select
Follow up to this question. I have the following code:
string[] names = new[] { "Bob", "bob", "BoB" };
using (MyDataContext dataContext = new MyDataContext())
{
foreach (var name in names)
{
string s = name;
if (dataContext.Users.SingleOrDefault(u => u.Name.ToUpper() == s.ToUpper()) == null)
dataContext.Users.InsertOnSubmit(new User { Name = name });
}
dataContext.SubmitChanges();
}
...and it inserts all three names ("Bob", "bob" and "BoB"). If this was Linq-to-Objects, it wouldn't.
Can I make it look at the pending changes as well as what's already in the table?
I don't think that would be possible in general. Imagine you made a query like this:
dataContext.Users.InsertOnSubmit(new User { GroupId = 1 });
var groups = dataContext.Groups.Where(grp => grp.Users.Any());
The database knows nothing about the new user (yet) because the insert wasn't commited yet, so the generated SQL query might not return the Group with Id = 1. The only way the DataContext could take into account the not-yet-submitted insert in cases like this would be to get the whole Groups-Table (and possibly more tables, if they are affected by the query) and perform the query on the client, which is of course undesirable. I guess the L2S designers decided that it would be counterintuitive if some queries took not-yet-committed inserts into account while others wouldn't, so they chose to never take them into account.
Why don't you use something like
foreach (var name in names.Distinct(StringComparer.InvariantCultureIgnoreCase))
to filter out duplicate names before hitting the database?
Why dont you try something like this
foreach (var name in names)
{
string s = name;
if (dataContext.Users.SingleOrDefault(u => u.Name.ToUpper() == s.ToUpper()) == null)
{
dataContext.Users.InsertOnSubmit(new User { Name = name });
break;
}
}
I am sorry, I don't understand LINQ to SQL as much.
But, when I look at the code, it seems you are telling it to insert all the records at once (similar to a transaction) using SubmitChanges and you are trying to check the existence of it from the DB, when the records are not inserted at all.
EDIT: Try putting the SubmitChanges inside the loop and see that the code will run as per your expectation.
You can query the appropriate ChangeSet collection, such as
if(
dataContext.Users.
Union(dataContext.GetChangeSet().Inserts).
Except(dataContext.GetChangeSet().Deletes).
SingleOrDefault(u => u.Name.ToUpper() == s.ToUpper()) == null)
This will create a union of the values in the Users table and the pending Inserts, and will exclude pending deletes.
Of course, you might want to create a changeSet variable to prevent multiple calls to the GetChangeSet function, and you may need to appropriately cast the object in the collection to the appropriate type. In the Inserts and Deletes collections, you may want to filter it with something like
...GetChangeSet().Inserts.Where(o => o.GetType() == typeof(User)).OfType<User>()...
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.