I have create a LINQ-to-SQL project in Visual Studio 2010 using Dynamic Data. In this project I have two tables. One is called phones_extension and the other phones_ten. The list of columns in phones_extension looks like this:
id, extension, prefix, did_flag, len, ten_id, restriction_class_id, sfc_id, name_display, building_id, floor, room, phone_id, department_id
In phones_ten it looks like this:
id, name, pbxid
Now, I'd like to be able to somehow make it so that there is an association (or inheritance?) that essentially results in me being able to make a query like phones_extension.ten and it gives me the result of phones_ten.name. Right now I have to get phones_extension.ten_id and then match that against phones_ten.id - I'm trying to get the DBML to handle this translation automatically.
Is this possible?
OK Dave, you need to setup a relatioship in the DB for this to work in Linq to SQL you could just create the relatioship (association in L2S) but there will need to be a primary key on each table anyway to allows edits.
Related
I have an application with a dataset linked to an sql server database. I have updated some of the names or foreign keys and primary keys in the sql server. How do I make those changes translate to the data set. For example, I had a primary key called fk_temsempl_xxxxx. I changed it to fk_temsempl on the sql database. How do I get that change to show in the dataset designer in visual studio?
I have tried running custom tool by right clicking on the dataset and clicking run custom tool. That didnt work. I tried configuring the table adapter of one of the tables where a change occured, but the name of the relation didnt change.
You actually just right click the relation and choose Edit Relation... or double click on the line (when the mouse cursor changes from arrow to drag symbol) but I honestly wouldn't bother; you'll then have further refactoring to do in the code anywhere the relation is used, and it can be heavily used by visual designers.
You also get the problem that VS may not help you with the refactoring: in data binding scenarios most things that can be a source of data can also be a collection of multiple things that can be a valid DataSource. They then rely on a string DataMember to determine which of the collections of data in the data source should be used for the data.
For example, when a bindingsource is bound to list a DataTable, the bindingsource.DataSource property might be the DataSet object that contains the DataTable, and thebindingsource.DataMemberis a string of "YOUR_TABLE_NAME". the BindingSource might not be bound asmyBindignSource.DataSource = myDataSet.MyDataTable`. Refactoring inside strings involves a find and replace
DataRelations in a DataSet are created from foreign keys as they were discovered when the relevant table(s) were added to the dataset but it is important to note that, like DataTables and everything else, they are NOTHING to do with the database schema objects at all - they aren't permanently associated with them, the dataset entities are just set up looking something like the database objects when they (dataset entities) are first created. DataTables are created from only those columns selected, and whatever .NET datatypes closely resemble the types output by the query. For a table of:
Person
------
Name VARCHAR(50)
SSN INTEGER
Birthdate DATE
If you created the table with SELECT * FROM Person you'd get a datatable with Name (string), SSN (int), Birthdate (datetime) but if you made a new datatable in the dataset based on SELECT LEFT(Name, 1) as Initial, PADLEFT(SSN, 20) as PadSSN, DATEDIFF(day, Birthdate, NOW()) as AgeDays FROM Person then you'd get a datatable of Initial (string), PadSSN (string), AgeDays (int) - i.e. the datatable looks nothing like the db table. This concept of disconnection between dataset and db is pervasive, and really the only things that relate in any way to the database are the properties that specify which DB table/column a particular DataTable/DataColumn relates to for purposes of loading/saving data. Your Person.Name datacolumn can be renamed to Blahblah, but it will still have a .SourceColumn property that is set to "Name" - that's how the mapping between dataset and db works; dataset is predominantly completely independent of the db. Renaming a DB column would require a change to the SourceColumn property only
DataRelations don't even have this notion of linking to the parent relation in the database; there's no SourceRelation or SourceFK proeprty because there is no need to. They're set up with the same rules and a generated name all based on the rules of the FK, but then they function independently and only within the dataset. If you rename or even remove an FK from the db the dataset will carry on working in the same restricted way it always did; adding a datarow to a child table when no aprent row exists for it will throw an exception - none of it anything to do with the FK in the db, and the DataRelation can have different rules to the FK (e.g it can cascade deletes when the FK is NOACTION) or even different columns. You can have more or fewer DataRelations than the DB has FKs
Run Custom Tool is not a "contact the DB and see what changes have occurred there and replicate them into the dataset", it is a "turn the XSD that describes the dataset into a bunch of C# classes that implement strongly typed dataset/table/relation/column etc objects". Any time you change the XSD by making an edit in the visual designer and hit save, the custom tool is run. If you edit the XSD directly in a text editor you may need to run it manually to have your changes reflected in c# classes
Reconfiguring a tableadapter probably won't do anything to the relations either; its solely concerned with changing the datatable and tableadapter. If you really want to refresh the relations, delete the datatable from the set and recreate it. Be prepared for a potentially significant mop up/refactoring of code
I am new to lightswitch as well as linq, i am using LS 2015. I want to know how to display the data of one table in other table's screen.
For example I have job vacancies, where I want to show candidate professional information who has applied for job. These two tables are related through Candidate personal ID, means a foreign key between candidate personal table and professional table.
The relation is as follows
JobVacancies->CandidatePersonalInfor->candidateProfessionalInfo. They are many to one related.
I have written a linq query to fetch data, where i have included some other tables also, my code is as follows
Any help is appreciated.
Have you defined the relationships you describe between the entities? If so, you'll have the ability to add and drop the details you require onto the form in the designer. The entities and their properties will be in the left pane of the screen designer.
If the join operation is more complex, you can use a WCF RIA Service to create a composite entity, as described in http://lightswitchhelpwebsite.com/Blog/tabid/61/EntryId/2226/Creating-a-WCF-RIA-Service-for-Visual-Studio-2013.aspx
I'm currently running in a multi-DB SQL Server environment and using linq to sql to perform queries.
I'm using the approach documented here to achieve cross DB joins:
http://www.enderminh.com/blog/archive/2009/04/25/2654.aspx
so basically:
2 data contexts - Users and Payments
Users.dbo.UserDetails {PK: UserId }
Payments.dbo.CurrentPaymentMethod { PK: UserId }
I drag the tables onto the DBML, and in the properties window, change the Source from dbo.UserDetails to Users.dbo.UserDetails to fully qualify the DB name.
I can then issue a single data context cross DB join by doing something like:
var results = (from user in datacontext.Table<UserDetail>()
join paymentmethod in dataContext.Table<CurrentPaymentMethod>() on user.UserId equals paymentmethod.UserId
... rest of query here ...);
Now this is tickety boo and works as I want it to. The only problem I'm currently having is when schema updates etc. happen (which is relatively frequent as we're in a significant dev phase).
(and finally, the question!)
What I want to achieve (and I've marked the question up as T4 as a guess, as I know that the DBML files are T4 guided) is an automated way when I drag any table onto a data context that the Source automatically picks up the DB name (so will have Users.dbo.UserDetails instead of just dbo.UserDetails)?
Thanks for any pointers :)
Terry
Have a look at the T4 Toolbox and the LinqToSql code generator it provides (Courtesy of Oleg Sych) - You can customize the templates to generate references however you'd like, but I think the problem you're going to run into is that the database name isn't stored in the dbml file.
What you could probably do is add a filter to the generator, perhaps using a dictionary or similar, such that in your .tt file, you maintain a list of tables and the databases they belong to. That way, if your maintenance task is to delete the class from the designer and drop it on again, it will get the right database name.
I have two projects using legacy databases with no associations between the tables. In one, if I create associations in the DBML file, I can reference the associations in LINQ like this:
From c In context.Cities Where c.city_name = "Portland" _
Select c.State.state_name
(assuming I added the link from City.state_abbr to State.state_abbr in the DBML file.)
In a different project that uses a different database, adding the association manually doesn't seem to give me that functionality, and I'm forced to write the LINQ query like this:
From c In context.Cities Where c.city_name = "Portland" _
Join s In context.States On c.state_abbr = s.state_abbr _
Select s.state_name
Any idea what I could be missing in the second project?
Note: These are completely contrived examples - the real source tables are nothing like each other, and are very cryptic.
Check your Error List page. You might have something like the following in there:
DBML1062: The Type attribute
'[ParentTable]' of the Association
element 'ParentTable_ChildTable' of
the Type element 'ChildTable' does not
have a primary key. No code will be
generated for the association.
In which case all you should need to do is make sure that both tables have a primary key set and re-save the dbml file. This will invoke the custom tool, which will in turn update the designer.cs file and create code for the association.
It looks like my problem was my tables didn't have primary keys in the second project. Like I stated, these are legacy tables, so I had to do the linking and primary key stuff in the Database Context instead of the database itself, and I just forgot to specify the primary keys the second time around. Frustrating when you don't spot it, but it makes sense now.
Sometimes, when everything is configured correctly but still not working, the solution can be as simple as restarting Visual Studio.
I don't know why it happens sometimes, but I thought I should add this answer because having done some searching for a solution myself, it seems nobody has suggested this yet...
I'm using Linq 2 Sql and I'd like to add a custom member on one of my data type. For example: I have tables Companies, Departments and Employees. Departments has a FK in Companies and Employess has a FK in Deparments. Very simple.
My goal is to add an EmployeeCount property on Company that will, of course, returns the number of employee in the company (by suming the number of employee in company's departments).
As you may know, it's really trivial to do: just add a member on the partial class and do the stuff. The problem is, I now want to sort on this custom member.
How can I write this custom member for Linq to be able to translate the logic into a valid SQL orderby? I tried with a SPROC but did not success.
Any help appreciated!
Fabian
I guess your may need to add this column to your schema, in order for SQL server to recognize it and take in under consideration in his optimizations.
I would have add a trigger that will update this column automaticly upon changes on your data.