I am abit curious about dbml.... Should I create one dbml file for one database or separated into different parts e.g. User dbml (only tables relate to users) etc? When I do this I will have abit of problems. Assume the User dbml has a User table and if the Order dbml has a User table as well, this won't be allowed if the entity namespace are the same. If I have set a different entity namespace for each of the dbml, it works but this will gives me a different entity of User table. When a single data returns to Business Logic layer, there is a difficulty of knowing which entity namespace of the user table to be used.
If I built one dbml file instead of having separate dbml, will single dbml appear slower than the separated dbml version when fetching the data from the database.
Linq to SQL is designed to be operated with a single Data Context object.
Lifetime of a LINQ to SQL DataContext
http://blogs.msdn.com/dinesh.kulkarni/archive/2008/04/27/lifetime-of-a-linq-to-sql-datacontext.aspx
The NerdDinner tutorial has a pretty good example of typical Linq to SQL usage, using a repository pattern. In all cases, the repository objects use a single Data Context object to perform the work:
http://nerddinnerbook.s3.amazonaws.com/Part3.htm
What you are trying to do sounds like it might be more suitable for the Entity Framework. Be advised, however, that the Entity Framework has some issues in its present release, particularly with regards to lazy loading.
Related
I have an application which is using Entity Framework 6 in order to interact with a SQL Server database. I have several migrations files due to the evolution of the application.
Now, I'd like to add the possibility to choice between a SQL Server database and a PostgreSQL database with keeping the same entity model.
When I apply the migrations files on SQL Server, all is ok.
But when I apply the same migrations files on PostgreSQL, it says that the database does not match the entity model and I have to generate a new migration file.
If I generate a new migration file, I see that it want to remove the property unicode on all string columns. I think it's because on PostgreSQL the type varchar (character varying) is able to store unicode and non unicode characters.
If I apply this migration file on PostgreSQL, all is ok now. But if I apply it on SQL Server, it say that the database does not match the entity model => columns varchar has been replaced per nvarchar.
I thought that the migrations files was able to adapt to the provider but apparently not.
For information, the property unicode is manage like that in the onModelCreating method :
modelBuilder.Entity<MyTable>()
.Property(e => e.ColumnName)
.IsUnicode(false);
So, my question is, do I have to manage different migration files depending on provider, knowing that I want to keep the same entity model ? If yes, how can I do this ?
Thanks a lot for your help
I have found a solution, I'm not sure it's the best but it's working.
In order not to be annoy anymore, I've created a batch migrations files per provider.
For that I've created one configuration per provider with specifying a specific context key and a different folder containing the migrations files.
This permits to switch between the different configurations depending of the current provider.
I have recently inherited a mess from the developer who used to sit in this chair over a year ago. One of the many things he did is create nearly identical tables in many databases (such as having a Users table in each database that contains exactly the same information). I am attempting to eliminate all the manual work that is currently being done every time a new employee is hired by eliminating these duplicate tables.
I have created a SQL view that represents data exactly as the old table did. It pulls it's data from the master database, but all the tables I need (and this new view) are all on the same DB. There is no need for the application I am working with to modify the users table, so it only needs read access (so a view should be fine, right?).
Is there any way to simply replace the table in code with the new view? I would be happy to provide more information if needed.
if the created view has the same name and same columns as the original table, it will work without app modification.
It is also possible to modify data throught this view (with some restrictions...), see https://msdn.microsoft.com/en-us/library/ms180800.aspx .
I'm creating a new visual studio web site using MVC4/webapi that will go against a database of 75 preexisting tables (not perfect in terms of foreign keys, etc.). I'm thinking that I will create an ado.net entity data model and select all my tables. then, when my tables change I will do the "update model".
With my linq2sql projects, I always ran sqlmetal against all my tables all the time to keep things in sync and that worked fairly well.
Is my plan to have all my tables in one ado.net entity data model reasonable? what pitfalls might I run into? Is it better to have lots of ado.net entity data models? I've tried having multiple ado.net entity models in other projects and I seem to constantly be getting my connection strings doubled in my web.config.
I did do a search on SO and did not find any discussions that directly addressed my concern.
If you followed your plan, you would miss out on an opportunity to have an entity model simpler than your database model:
Your application almost certainly doesn't need all 75 tables.
You would be missing the opportunity to consider a series of 1-1 tables as a single entity
You would be missing the opportunity to use inheritance in your model
You would be missing the opportunity to keep junction tables out of your model
You would be losing one of the greatest advantages of Entity Framework over LINQ to SQL: it does not need to stay one-to-one with the database.
I am working on a asp.net mvc project and using Linq for all my data related operations. In such cases, do I need to define relationship in the SQL Server database ??
I am using Entity framework and Linq so I think it doesn't matter if I create an E-R diagram(i.e defining relationship) or not.
By 'define relationship' I assume you mean 'Foreign key constraints'. It is always advisable to define constraints in order to maintain data integrity. You should also consider that the database for your project could probably be used by other applications in the future which might be based on other technologies than EF.
If you have relations in DB they will automatically be imported in your EF Model but you always have an option to create the associations manually in the EF Designer if you don't have relations in DB.
See How to manually add association in Entity Framework
We are in the process of a multi-year project where we're building a new system and a new database to eventually replace the old system and database. The users are using the new and old systems as we're changing them.
The problem we keep running into is when an object in one system is dependent on an object in the other system. We've been using views, but have run into a limitation with one of the technologies (Entity Framework) and are considering other options.
The other option we're looking at right now is replication. My boss isn't excited about the extra maintenance that would cause. So, what other options are there for getting dependent data into the database that needs it?
Update:
The technologies we're using are SQL Server 2008 and Entity Framework. Both databases are within the same sql server instance so linked servers shouldn't be necessary.
The limitation we're facing with Entity Framework is we can't seem to create the relationships between the table-based-entities and the view-based-entities. No relationship can exist in the database between a view and a table, as far as I know, so the edmx diagram can't infer it. And I cannot seem to create the relationship manually without getting errors. It thinks all columns in the view are keys.
If I leave it that way I get an error like this for each column in the view:
Association End key property [...] is
not mapped.
If I try to change the "Entity Key" property to false on the columns that are not the key I get this error:
All the key properties of the
EntitySet [...] must be mapped to all
the key properties [...] of table
viewName.
According to this forum post it sounds like a limitation of the Entity Framework.
Update #2
I should also mention the main limitation of the Entity Framework is that it only supports one database at a time. So we need the old data to appear to be in the new database for the Entity Framework to see it. We only need read access of the old system data in the new system.
You can use linked server queries to leave the data where it is, but connect to it from the other db.
Depending on how up-to-date the data in each db needs to be & if one data source can remain read-only you can:
Use the Database Copy Wizard to create an SSIS package
that you can run periodically as a SQL Agent Task
Use snapshot replication
Create a custom BCP in/out process
to get the data to the other db
Use transactional replication, which
can be near-realtime.
If data needs to be read-write in both database then you can use:
transactional replication with
update subscriptions
merge replication
As you go down the list the amount of work involved in maintaining the solution increases. Using linked server queries will work best if its the right fit for what you're trying to achieve.
EDIT: If they're the same server then as suggested by another user you should be able to access the table with servername.databasename.schema.tablename Looks like it's an entity-framework issues & not a db issue.
I don't know about EntityToSql but I know in LinqToSql you can connect to multiple databases/servers in one .dbml if you prefix the tables with:
ServerName.DatabaseName.SchemaName.TableName
MyServer.MyOldDatabase.dbo.Customers
I have been able to click on a table in the .dbml and copy and paste it into the .dbml of the alternate project prefix the name and set up the relationships and it works... like I said this was in LinqToSql, though have not tried it with EntityToSql. I would give it shot before you go though all the work of replication and such.
If Linq-to-Entities cannot cross DB's then Replication or something that emulates it is the only thing that will work.
For performance purposes you probably want either Merge replication or Transactional with queued (not immediate) updating.
Thanks for the responses. We're going to try adding triggers to the old database tables to insert/update/delete records in the new tables of the new database. This way we can continue to use Entity Framework and also do any data transformations we need.
Once the UI functions move over to the new system for a particular feature, we'll remove the table from the old database and add a view to the old database with the same name that points to the new database table for backwards compatibility.
One thing that I realized needs to happen before we can do this is we have to search all our code and sql for ##Identity and replace it with scope_identity() so the triggers don't mess up the Ids in the old system.