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...
Related
I am using an Oracle database to generate my EF entities and context.
I do not have control over schema, its all provided by client, and I strictly can't change anything over there.
I have to generate entities for various Views.
When I do this, it is adding all non-nullable columns as the keys (as I can see while opening the edmx in XML editor).
How can I specify which columns should be used as keys? Can I do anything in at EF level without changing the schema?
Ok, I found the solution. We can do this in EF. Select each column in entity, and Set "Entity Key" to "True/ False".
My MVC2 app use LINQ to SQL as the ORM. I just drag and drop the tables from the SQL Server Explorer connection to the LINQ design surface. Two of the tables (A and B) are related. Table A has 3 foreign keys referencing Table B. In the LINQ design surface, I manually change the name of the parent property for these associations to give them more distinguished names. However, whenever I modify the table structure in the SQL Server, and drag and drop the new structure to LINQ, I would lose the names. Is there a way to prevent this from happening? Thanks.
No. When you drag the tables back to the designer, Linq to SQL regenerates the code in the partial class, obliterating your custom changes.
The only way to preserve the name change is to rename the affected table fields in the database.
You might be able to achieve such customization preservation with the T4 Toolbox.
It is always a bad idea to make the associations at the LINQ level. Make the associations at the table level. This will ensure that when ever you are doing a drag and drop of the tables, the designer class reflects the correct associations.
I am currently working on a project where we are rewriting software that was originally written in Visual DataFlex and we are changing it to use SQL and rewriting it into a C# client program and a C#/ASP.Net website. The current database for this is really horrible and has just had columns added to table or pipe(|) characters stuck between the cell values when they needed to add new fields. So we have things like a person table with over 200 columns because stuff like 6 lots of (addressline1, addressline2, town, city, country, postcode) columns for storing different addresses (home/postal/accountPostal/ect...).
What we would like to do is restructure the database, but we also need to keep using the current structure so that the original software can still work as well. What I would like to know is would it be possible using Linq to write a DataContext Object Model Class that could sort of interpret the data base structures so that we could continue to use the current database structure, but to the code it could look like we where using the new structure, and then once different modules of the software are rewritten we could change the object model to use the correct data structure???
First of all, since you mention the DataContext I think you're looking at Linq to SQL? I would advice to use the Entity Framework. The Entity Framework has more advanced modeling capabilities that you can use in a scenario as yours. It has the ability to construct for example a type from multiple tables, use inheritance or complex types.
The Entity Framework creates a model for you that consists of three parts.
SSDL which stores how your database looks.
CSDL which stores your model (your objects and the relationships between them)
MSL which tells the Entity Framework how to map from your objects to the database structure.
Using this you can have a legacy database and map this to a Domain Model that's more suited to your needs.
The Entity Framework has the ability to create a starting model from your database (where all tables, columns and associations are mapped) en then you can begin restructuring this model.
These classes are generated as partial so you could extend them by for exampling splitting the database piped fields into separate properties.
Have you also thought about using Views? If possible you could at views to your database that give you a nicer dataschema to work with and then base your model on the views in combination with stored procedures.
Hope this gives you any ideas.
I have a View in an SQL Server Database, which involves many different tables. I am using Linq to Entities to access the database, so I have no problem getting and showing view's result.
But the problem is when I want to modify some field in those results. As long as a view doesn't have a primary key, the Entity is read-only, so the question is:
Is there any way to modify the object with the view's data and save those changes in the corresponding tables?
Sorry for my english, but it's not my native language.
Thank you very much in advance!
There are some requirements for VIEW to be updatable. Take a look here. You say your view references many tables, so you have to implement INSTEAD OF trigger.
I have three tables Projects, Users and ProjectMembers. The ProjectMembers table is a mapping table and has only two columns ProjectId and UserId.
In my object model i have two classes Project and User. The Project class has a property IEnumerable<User> Members
I am using an external xml map file for mapping linq to sql associations. I am able to get the Project and the User data but I dont know how to map the Members association.
This sounds like a Many-to-Many mapping (Projects <-> Users).
In which case you are going to run into problems using Linq To SQL. To cut a long story short it does not really support that mapping. There are several workarounds which you can find on google, one of which is altering the partial class to provide the access to the Members/Projects collection on the Project and User classes respectively.
e.g. http://www.iaingalloway.com/2015/06/many-to-many-relationships-in-linq-to-sql.html