I generated model from existing database in c# via entity framework, but when i change database (for example add column to table) application stop work, because in model miss the new column, but i don´t need the new column. Is there any solution to generate model from database, but do not be independent to change in db?
Thanks.
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I'm pretty new to Entity Framework: I started from a database-first model to maintain an application created using a strange mixture of EF and plain old SQL.
I created my own fresh DB-first model and I'm fine with it. Today my boss asked me to add a new entity. Lack of foreign keys simplifies the scenario.
I have created my new entity in the diagram (it's made of three instances of a Complex Entity I just created) but now I have to make an incremental DB script to create the new table. I'm supposed to do that both for MySQL and SQL Server but let's start with the second.
So now I see that I have a compilation problem "No mapping for entity Entity" and if I use "Update model from database" command I see no option for pushing changes to DB, but that sounds correct given the word "from".
OK, I have tried to click "Table Mapping" from the right-click menu and I found the option to map the entity to the table. I was going to type the new table name in the "Add table or view" field and... WAIT! I can only select existing tables
I understand it's just for a single table so I can simply "Generate database from model" in order to get the full SQL script, find the table I want, run that to DB and "Update model from DB" so EF will see the table, BUT
I would like to understand how to create incremental scripts with Entity Framework. That is my question.
You indicate you have a database-first design but appear to be working from a code-first mindset.
In database-first design the entity model is subordinate the underlying datastore. Changes to the model (or at least changes to the model which also require changes to the underlying datastore) occur FIRST on the database.
So how do you create a new table for the entity? You create the new table in your database (CREATE TABLE ...). Then using the "Update Model From Database" wizard you select the new table from the "Add" tab. EF will create the corresponding EF class automatically. If you already manually created the entity you should delete it otherwise you could end up with some weird entity naming (i.e. Customer1).
Database first does not have the capability to support table creation at the entity layer. Changes to the database are always one way, from the database to the entity model, hence the term "database first".
On the other hand if you are more comfortable creating entities directly and want to build a database from a set of entities you should be looking to create a "Code-First" design. Despite the name "code first" it is possible to get an initial set of entity classes from an existing database. The term "code first" refers to the origination of changes to the db/model structure.
I am using CodeFirst approach, EF 4.0. I have model of tables that application uses. However I want to use another database as encyclopedia, meaning this database has a lot of data and these data is interconnected by foreign key. I have declared DbSet of my external datebase. However when model is generated, all entities that has to exist within my external DB, are placed as empty tables in my main DB. So here is the question. How can I specify for some entities to use external DB while for other use main DB?
We want to update a ADO.Net Entity Data Model programmatically, so that the EDM is getting the newest version of the database (new tables, values etc.). I want to have a complete update of all stuff.
I know that it is possible to update the EDM, by clicking in the Model Designer, Update Model from Database.
Do you know any solution?
Thank you in advance.
I have my database already set, I want to add a new field to the model, a new column to the table, is there a way I can do this without losing all my data?
Normally if you delete the DB it will recreate everything automatically but I don't want to lose the data.
I'm using SQL Server 2008 as database.
You will need to use EF Migrations to add the new column to your database. You can read more about EF Migrations here and here.
If you're using code first, I've always just added the column to the database manually in situations like that. Unfortunately, there is no simple way to automate incremental model updates with Code First.
For example, one of EF Code First's own errors even specify manual update as the best option:
The model backing the ‘your context’ context has changed since the database was created. Either manually delete/update the database, or call Database SetInitializer with an IDatabaseInitializer instance. For example, the DropCreateDatabaseIfModelChanges strategy will automatically delete and recreate the database, and optionally seed it with new data.
Suppose I have an existing database set up using Entity Framework. Is there a mechanism through which I can safely add or remove entities (or their properties) such that the database is altered automatically?
I know there's an option to "Update Model From Database". Is there an equivalent "Update Database From Model" ? Is there a way to configure Visual Studio to do this automatically?
Entity Framework 4.3 has Code First Migration support.
EF helps you with checking the differences between your code and database and then generates code for you that handles this changes. You can use the NuGet package manager console to enable migrations, add a new migration and run them against your database (or create a sql script).
This blog explains how the Migrations work and this blog shows how you can use it with an existing database
Altering the database schema isn't a straightforward operation (has a column been renamed, or is it new column? Can the old type be converted to the new type?) that you can easily infer from the model.
EF doesn't alter the tables for you - it can Drop-Create the DB for you when you change it. However, if you change the existing database by hand to suit the model, EF doesn't seem to mind. It looks like what they check for is Hash(Model) = Hash(Tables).