I have a linq sql class i.e."Customer". I want to implement the features like User Defined Fields. Can you please tell me how can I create dynamic column into this class? How can I access this column from Customer object?
Related
My intent is to create a generic (not in C# meaning) database model for Windows Phone using linq to sql. User of such model should be able to pass an array of his data object types (classes marked with Table attribute) to model's contstructor, and then model should take care about adding related tables to database and provide API for CRUD operations.
But then I've found out that in order to add tables to database, your data context (class inherited from DataContext class) have to declare each table as a property! That's embarrassing. Does this fact mean that my idea is not implementable? Because I obviously cannot add properties to my DataContext-based in the runtime.
So my question is, am I right in my judgments? If yes, are there some workarounds to solve this issue?
Thanks in advance.
EDIT: better question tagging, for somebody finally notice this.
You do not need to use a strongly typed DataContext (a class inheriting from DataContext and declaring properties for each table). You can do something like the following instead
var context = new DataContext("connection string", new AttributeMappingSource());
var table = context.GetTable<T>();
where T is some type marked with the Table attribute.
Summary of the question: How do i scaffold two or more tables with linq to entities.
I cant find an example; they always scaffold only one table.
Details:
If I have two tables and I use LINQ to entities with a t4 template for dbcontext capability like such:
Table1
Name LastName PositionId
Jose j 1
Table2
PositionPrimaryKey PositionId PositionDescription
1 1 MainProgrammer
If I had these table mapped with linq to entities how would I scaffold them?
Then i put Table1 as my Model class.
I have my employeesentities as dbcontext
But that only creates the values for table 1 and not 2.
If I create a new model that contains both entities, it says is not part of Employeeentities and the class could not be modfied to add my new entity.
So, you have a 1:1 relationship between these tables? If yes, I suggest you creating an entity by hand, set its defining query to the necessary join, and map Insert/Update/Delete to stored procedures in the Mapping Details screen. It involves some (quite simple) sql, but it is the cleanest way for your code above.
If it's not a 1:1 relationship, you need to modify the t4 template to conditionally create the fields of the linked property (it has to navigate the property, and based on some condition, like you say "if property is called Table2", create the extra fields). If you have already done so and it doesn't work, maybe there's something going on with the selection of properties used by MVC scaffolding. It might use reflection and choose only primitive types.
I have a class hierarchy mapped into one table. There is one superclass and 8 different sub classes. A lot of my queries needs to fetch e.g. 2 of the sub classes only for a specific date.
The table has a discriminator column that nhibernate itself uses. But when using LINQ for querying it is not possible to use this discriminator as there is no property for it.
Is there a commonly used trick for only fetching specific sub class when using nhibernate ?
For now I first have Linq 4 Nhiberneate query that fetches all sub classes into a given period. And then uses Linq 4 objects to filter on the sub classes that I need.
Is it possible to expose the discriminator column of the table as a property and thereby be able to make a where clause on it ?
In Hql querying subclasses is done by class, so you'd do
from subclass
where subclass.DateTime = :myDateTime
The docs also say you can query hierarchies by the special class property, eg:
from Eg.Cat cat where cat.class = Eg.DomesticCat
I don't know if this is possible with the Criteria API or NH Linq Provider.
You could always get all the instances with the correct time, and then filter client side, eg:
var allCandidates = from super in session.Linq<SuperClass>()
where super.Date > DateTime.Now.AddDays(-1)
select super
var results = from candidate in allCandidates
where candidate.GetType() == typeof(SubClass)
select candidate
It's a bit nasty, and if the subset of classes you're querying is always the same, you might be better off inserting another class in the hierarchy and querying that.
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.
Have been trying out the new Dynamic Data site create tool that shipped with .NET 3.5. The tool uses LINQ Datasources to get the data from the database using a .dmbl context file for a reference. I am interseted in customizing a data grid but I need to show data from more than one table. Does anyone know how to do this using the LINQ Datasource object?
If the tables are connected by a foreign key, you can easily reference both tables as they will be joined by linq automatically (you can see easily if you look in your dbml and there is an arrow connecting the tables) - if not, see if you can add one.
To do that, you can just use something like this:
<%# Bind("unit1.unit_name") %>
Where in the table, 'unit' has a foreign key that references another table and you pull that 'unit's property of 'unit_name'
I hope that makes sense.
(EDIT misunderstood the question, revising my answer to the following)
Your LinqDataSource could point to a view, which allows you to overcome the problem of not being able to express a Join in the actual element. From "How to: Create LINQ to SQL Classes Mapped to Tables and Views (O/R Designer)":
The O/R Designer is a simple object relational mapper because it supports only 1:1 mapping relationships. In other words, an entity class can have only a 1:1 mapping relationship with a database table or view. Complex mapping, such as mapping an entity class to multiple tables, is not supported. However, you can map an entity class to a view that joins multiple related tables.
You cannot put more than one object/datasource on a datagrid. You will have to build a single ConceptObject that combines the exposed properties of the part Entities. Try to use DB -> L2S Entities -> ConceptObject. You must be very contrived if the DB model matches the ConceptObject field-for-field.
You are best using a ObjectDataSource when you wnt to do more complex Linq and bind your Grid to the ObjectDataSource.
You do however need to watch out for Anonymous types that could give you some trouble, but anything is posible...