I'm using EF6 and need to modify my code to use views instead of tables. I've have found a few questions/answers posted on how to modify the .edmx so that the views will act as tables that have an association with them. Most of the responses are quite old and I was wondering if there was an easier way available now that can be used? For example say you are using the 2 tables from the Northwind database (Categories and Products). How would modify the .edmx if now the are wrapped in a view (vCategories and vProducts). hopefully, there is an easier way than making all these edits.
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I'm using Entity Framework 4.3 and I'd like to create a view because of the low performance of some selects. Is possible to do it from code?
Peter Kellner has mentioned in his article:
With CodeFirst, making views is problematic because you are not actually creating your own tables and columns so going directly into the database is really not something you should do. Creating a view basically violates one of the main purposes of CodeFirst which is to remove you from having to see database details. Making a view now tightly binds your model to that view and if you change you model and not the view you are in for trouble.
For more information visit Entity Framework Code First From Microsoft, Best and Worst Practices and How do I define a database view using Entity Framework 4 Code-First?
I am just getting into Entity Framework for the first time beyond simple examples.
I am using the model-first approach and am querying the data source with LINQ-to-Entities.
I have created an entity model that I am exposing as an OData service against a database where I do not control the schema. In my model, I have two entities that are based off of two views in this database. I've created an association between the two entities. Both views have a column with the same name.
I am getting the error:
Ambiguous column name 'columnname'. Could not use view or function 'viewname' because of binding errors.
If I was writing the SQL statement myself, I'd qualify one of the column names with an alias to prevent this issue. EF apparently isn't doing that. How do I fix this, short of changing the view? (which I cannot do) I think this does have something to do with these entities being mapped to views, instead of being mapped to actual tables.
Assuming you can change the model have you tried going into the model and just changing one of the column names? I can still see how it might be problematic if the two views are pulling back the same column from the same table. I can tell that when working directly with a model mapped to tables, having identically named columns is not a problem. Even having multiple associations to the same table is handled correctly, the Navigation Properties are automatically given unique names. Depending on which version of EF you used you should be able to dig into the cs file either under the model or under the t4 template file and see what's going on. Then you can always create a partial class to bend it to your will.
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.
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...