I have a table in the database with the following columns: ID, Name, Txt. We are using Linq To Sql to implement our DAL. In there another collegue added two extra columns so in the code the same table results: ID, Name, Txt, NameTemp, TxtTemp.
These two "fake" tables are used in different parts of the code in LINQ joins and analyzing with SQL Profiler the parsed SQL query takes the "real" columns and everything works properly.
Now I need to make an INSERT using that table, but I get an exception since also the fake columns are used in the statement.
Since I cannot add the two fake columns in the DB(since unuseful there), is there a way in which I could make an insert with Linq omitting these two columns?
I think i know where you're getting at. You should be able to add properties to a partial linq class no problem, only thing is that if you try and use a linq query against these "fake" columns, you'll get an exception when linqtosql tries to reference a column that doesn't exist in the database. I've been through this before - i wanted to be able to select columns that don't exist in the database (but do in the linq2sql dbml class) and have linq2sql translate the columns into what they really are in the database. Only problem is that there's no real easy way to do this - you can add attributes to the "fake" properties so that linq2sql thinks that NameTmp and TxtTmp are in fact Name and Txt in the sql world, only problem is that when it comes to inserting a record, the translated sql specifies the same column twice (which SQL doesn't like and throws an exception).
You can mark the column with IsDbGenerated = true - that'll let you insert records without getting the double column problem, but you can't update a record without linqtosql complaining that you can't update a computed column. I guess you can use a sproc to get around this perhaps?
I logged a bug with Microsoft a while back, which they'll never fix. The info here might help you get what you need -
http://social.msdn.microsoft.com/Forums/eu/linqtosql/thread/5691e0ad-ad67-47ea-ae2c-9432e4e4bd46
https://connect.microsoft.com/VisualStudio/feedback/details/526402/linq2sql-doesnt-like-it-when-you-wrap-column-properties-with-properties-in-an-interface
LINQ is not for inserting data, but for querying only - Language INtegrated Query. Use ADO.NET for inserting the data.
(Leaving the first part to remind my stupidity)
Check ScottGu. The classes generated are partial (mentioned here), so you can put your 2 properties into the editable part and since they won't have any mapping attribute defined, they won't be mapped nor persisted.
Related
I have a linq query that gets data from an OData Reporting service
So far so good, but when I return my data like this :
select new {TimesheetActual , TimesheetLine,Timesheet, TimesheetProject,TimesheetTask, subTv, TimesheetResource, subRes, pLeft}
It returns as a collection of nested collections.
For my service I need one big table with every column from every record.
I know this is possible by explicitly naming every column in the select statement like this:
select new { TimesheetActual.Column1, TimesheetActual.Column2, .., TimesheetLine.Column1,.., TimesheetProject.Column1,..}
But due to the massive amount of columns I'm a little reluctant to do it this way.
So my question, is there any way to either merge the collections or another way to get the same result without having to specify 100+ columns?
I'm teaching myself Delphi database programming using a MySQL database. I'm trying to add a record from a nested ClientDataSet with the link between master and detail tables an autoincrement field in the master table. I found a question/answer pair that appears to answer my question at: Inserting records with autoincrementing primary keys
The thing I don't understand is setting the required flag in the Query. I can't figure out how to do that as I'm too inexperienced, nor do I understand why it is necessary.
Similar to the question linked above, I have a
(SQLConnection->TSQLDataSet->DataSetProvider->ClientDataSet using dbexpress.
| |->LinkDataSource
->TSQLDataSet2->LinkDataSource
I load data into my nested ClientDataSet fine, so the component links to create the nested structure work. After loading the master/detail tables into the nested dataset, the following code gives an error.
MasterCDS1.Append;
MasterCDS1.FieldByName('TLNo').Required := False;
MasterSDS.FieldByName('TLNo').Required := False; { Error: Field 'TLNo' not found }
MasterCDS1.FieldByName('TLNo').ProviderFlags := [pfInWhere, pfInKey];
{ ... Populate Master table Fields}
MasterCDS1.Post;
MasterCDS1.ApplyUpdates(0);
TLNo is the field linking the tables and part of the primary key of the master table, and part of the primary key of the detail table. The third line where I try to set the TSQLDataSet generates the error shown in the comment. MasterSDS is where I put my 'Select * from master' query. MasterCDS learns the Schema from this query and that the field TLNo is a required field in both master and detail MySQL tables. That third line of code is my "interpretation" of what Mr Uwe Raabe said to do. Clearly I did this wrong. Can someone provide a code example so that this Delphi noob won't misinterpret the instructions? Thanks in advance.
The only reason I can imagine for the error you describe is that MasterSDS is not open when you execute that third line. "Field not found" raises either when the field does not exist in the table or the dataset (i.e. query in this case) is not open and has no static fields defined.
This leads to another point I want to mention: place the Required and the ProviderFlags settings in the AfterOpen event of the corresponding dataset. There is no need to repeat these settings whenever you append a record. If you work with static fields you can even do these settings in the Object Inspector.
For being a starter I suggest you always use static fields which can be adjusted inside the IDE. This will simplify things significantly.
I have a regular view in sql server 2008 and I`m using entity framework generate design from database approach. I already know about the keys issues for views in entity framework but that is not my solution. When I query select * from view, it brings out 3 rows which is right, but all the rows are the same and are the first row in the database view.
some help would be very appreciated.
I already know about the keys issues for views in entity framework but that is not my solution. When I query select * from view, it brings out 3 rows which is right, but all the rows are the same and are the first row in the database view.
What you describe is exactly the problem caused by incorrect key. Your three rows must have unique identification - some column or set of columns must uniquely identify each possible returned record. These columns must be set as entity key in the designer.
You can also avoid this issue by not using change tracking when loading data from the view because returned entities are read-only. You have to use MergeOption.NoTracking for that ObjectSet:
context.MyViewEntities.MergeOption = MergeOption.NoTracking;
var data = context.MyViewEntities.ToList();
I have a question related to this one. I don't want to do a calculation (aggregation), but I need to get display values from an association. In my C# code, I can directly reference the value, because the foreign key constraint made Linq generate all the necessary wiring.
When I specify the IQueryable as the Gridview datasource property, and reference something that is not a column of the primary entity in the result set, I get an error that the column does not exist.
As a newbie to Linq, I am guessing the assignment implicitely converts the IQueryable to a list, and the associations are lost.
My question is, what is a good way to do this?
I assume that I can work around this by writing a parallel query returning an anonymous type that contains all the columns that I need for the gridview. It seems that by doing that I would hold data in memory redundantly that I already have. Can I query the in-memory data structures on the fly when assigning the data source? Or is there a more direct solution?
The gridview is supposed to display the physician's medical group associations, and the name of the association is in a lookup table.
IQueryable<Physician> ph =
from phys in db.Physicians
//from name in phys.PhysicianNames.DefaultIfEmpty()
//from lic in phys.PhysicianLicenseNums.DefaultIfEmpty()
//from addr in phys.PhysicianAddresses.DefaultIfEmpty()
//from npi in phys.PhysicianNPIs.DefaultIfEmpty()
//from assoc in phys.PhysicianMedGroups.DefaultIfEmpty()
where phys.BQID == bqid
select phys;
(source: heeroz.com)
So, based on Denis' answer, I removed all the unneeded stuff from my query. I figured that I may not be asking the right question to begin with.
Anyways, the page shows a physician's data. I want to display all medical group affiliations in a grid (and let the user insert, edit, and update affiliations). I now realize that I don't need to explicitly join in these other tables - Linq does that for me. I can access the license number, which is in a separate table, by referencing it through the chain of child associations.
I cannot reference the medical group name in the gridview, which brings me back to my question:
AffiliationGrid.DataSource = ph.First().PhysicianMedGroups;
This does not work, because med_group_print_name is not accessible for the GridView:
A field or property with the name 'med_group_print_name' was not found on the
selected data source.
Again, bear with me, if it is all too obvious that I don't understand Linq ... because I don't.
Your query seems strange. You should try to simply display
ph = from phys in db.Physicians
where phys.BQID == bqid
select phys;
in your grid. That should work.
Also, why the calls to Load()? If the DataContext is not disposed when the grid is binding, you should not need it.
If you still have issues, can you please post the error message you get, that would help...
Part 2
The problem is that you have the name is effectively not in the PhysMedGroup. You need to navigate one level down to the MedGroupLookup to access the name, since it is a property of that class.
Depending on the technology you are using (it seems to be either WinForms or Web Forms), you will need to configure your data-binding to access MedGroupLookup.med_group_print_name.
I am trying to inherit from my generated datacontext in LinqToSQL - something like this
public class myContext : dbDataContext {
public System.Data.Linq.Table<User>() Users {
return (from x in base.Users() where x.DeletedOn.HasValue == false select x);
}
}
But my Linq statement returns IQueryable which cannot cast to Table - does anyone know a way to limit the contents of a Linq.Table - I am trying to be certain that anywhere my Users table is accessed, it doesn't return those marked deleted. Perhaps I am going about this all wrong - any suggestions would be greatly appreciated.
Hal
Another approach would to be use views..
CREATE VIEW ActiveUsers as SELECT * FROM Users WHERE IsDeleted = 0
As far as linq to sql is concerned, that is just the same as a table. For any table that you needed the DeletedOn filtering, just create a view that uses the filter and use that in place of the table in your data context.
You could use discriminator column inheritance on the table, ie. a DeletedUsers table and ActiveUsers table where the discriminator column says which goes to which. Then in your code, just reference the Users.OfType ActiveUsers, which will never include anything deleted.
As a side note, how the heck do you do this with markdown?
Users.OfType<ActiveUsers>
I can get it in code, but not inline
Encapsulate your DataContext so that developers don't use Table in their queries. I have an 'All' property on my repositories that does a similar filtering to what you need. So then queries are like:
from item in All
where ...
select item
and all might be:
public IQueryable<T> All
{
get { return MyDataContext.GetTable<T>.Where(entity => !entity.DeletedOn.HasValue); }
}
You can use a stored procedure that returns all the mapped columns in the table for all the records that are not marked deleted, then map the LINQ to SQL class to the stored procedure's results. I think you just drag-drop the stored proc in Server Explorer on to the class in the LINQ to SQL designer.
What I did in this circumstance is I created a repository class that passes back IQueryable but basically is just
from t in _db.Table
select t;
this is usually referenced by tableRepository.GetAllXXX(); but you could have a tableRepository.GetAllNonDeletedXXX(); that puts in that preliminary where clause to take out the deleted rows. This would allow you to get back the deleted ones, the undeleted ones and all rows using different methods.
Perhaps my comment to Keven sheffield's response may shed some light on what I am trying to accomplish:
I have a similar repository for most
of my data access, but I am trying to
be able to traverse my relationships
and maintain the DeletedOn logic,
without actually calling any
additional methods. The objects are
interrogated (spelling fixed) by a StringTemplate
processor which can't call methods
(just props/fields).
I will ultimately need this DeletedOn filtering for all of the tables in my application. The inherited class solution from Scott Nichols should work (although I will need to derive a class and relationships for around 30 tables - ouch), although I need to figure out how to check for a null value in my Derived Class Discriminator Value property.
I may just end up extended all my classes specifically for the StringTemplate processing, explicitly adding properties for the relationships I need, I would just love to be able to throw StringTemplate a [user] and have it walk through everything.
There are a couple of views we use in associations and they still appear just like any other relationship. We did need to add the associations manually. The only thing I can think to suggest is to take a look at the properties and decorated attributes generated for those classes and associations.
Add a couple tables that have the same relationship and compare those to the view that isn't showing up.
Also, sometimes the refresh on the server explorer connection doesn't seem to work correctly and the entities aren't created correctly initially, unless we remove them from the designer, close the project, then reopen the project and add them again from the server explorer. This is assuming you are using Visual Studio 2008 with the linq to sql .dbml designer.
I found the problem that I had with the relationships/associations not showing in the views. It seems that you have to go through each class in the dbml and set a primary key for views as it is unable to extract that information from the schema. I am in the process of setting the primary keys now and am planning to go the view route to isolate only non-deleted items.
Thanks and I will update more later.