We are upgrading an old VB6 application which sits on a SQL Server 2005 database, to an Entity Framework solution. The database remains the same, except - we're adding a new table. Is it possible with Entity Framework, to maintain the existing structure, when it gets installed on a client PC - and just add one new table?
Is this how Code First will work? Can I be 100% certain that no other tables will be modified?
i don't think, the effort is worth it to switch to code-first if you have an existing database and want to add only one table.
it is possible to map code-first classes to an existing database (reverse engineer code first). actually, i'm not very experienced with that workflow, but i know you can. You have to deal with a lot of manual mapping (with DataAnnotations or Fluent API), so in your case i would recommend to use the Entity Framework Database First workflow, since adding a single table saves you a lot of work.
this link has some useful information: Arthur Vickers Blog - Don't use Code first by mistake
You have two options, use a database editor such as SQL management studio to create the table which you can then map to a ef entity, or use migrations for ef which will let you update your database via ef.
Take a look at the migrations tutorial here: http://msdn.microsoft.com/en-gb/data/jj591621
I am using the database first approach, since a database developing team is doing the changes I require in the database on the SQL server for me.
Hence, I have to update the EDMX whenever the schema in the database changes.
Note: Changing one single table directly does not work for me, because VS doesn't always detect the changes right (for this issue, here are some details in SO if you're interested).
Hence, I am using the following workaround (regenerating all the tables):
In VS 2012, open the EDMX file by double-clicking on it. The graphic representation of the tables is shown.
Left-Click into the EDMX designer, then select all tables by pressing CTRL+A. Then, remove them by pressing DEL.
Right-Click into the EDMX designer and select "Update Model from Database ..." in the context menu.
The Update Wizard opens. In the "Add" tab, check "Tables", and depending on the requirements, check "Pluralize or singularize generated object names", "Include foreign key columns in the model" and optionally "Import selected stored procedures and functions into the entity model". Usually, I am using the "Pluralize..." and "Include foreign key columns..." options.
Click Finish. Now Save by pressing Ctrl+S.
That workaround works fine for me, and requires just a minute to update the model reliably.
Related
I am working on a project which is using Entity Framework code first for its data structure. It was created with code first, but was never migrated again and only has its initial migration data stored. Since then, the database has been modified directly through server explorer in VS2015.
There is no migration information about any changes and the database has critical information which I cannot lose.
Which brings me to my Questions.
If I create a new migration and update the database from it, will it wipe all changes which were not recorded in migrations and still leave the changes which were made as well?
The details of your question is a bit sketchy, but I will make some assumptions in order to help you along. Please correct where I am wrong.
I assume that you want to keep the data which resulted from the changes which were effected directly to the database, but you do not want to keep the changes that was effected to the database - in other words: keep the data but not the datastructures.
My advice is as follows
Always perform a full backup of your database when you are about to do something you are uncertain about.
If you can identify the tables you want to update, you can always use the SELECT INTO statement to create a quick backup of the specific tables only. These tables will not be removed when you do a EF database migration unless you explicitly script the deletion.
You can build the SELECT INTO statement into your EF migration via the Sql() method, or you can manually run the command against the database.
More information:
Click here to learn about EF code first migrations in general
Click here for a comprehensive code first migration reference
I believe following two posts will help you.
EF 4.3 Migration Walkthrough : http://blogs.msdn.com/b/adonet/archive/2012/02/09/ef-4-3-code-based-migrations-walkthrough.aspx
update:
Code First Migrations with an existing database
https://msdn.microsoft.com/en-us/data/dn579398.aspx
We have to maintain a very old application.
There is an old part (all data access is handled with stored procedures) and since my predecessors took over the application, they started to build a new part for the new requirements which uses entity framework 6.
Now the customer has a new requirement that needs access to one of the tables for which there isn't an EF-model yet.
Is there an easy way to automatically create an EF-model from an existing database table? (I only want this one table, not the whole remaining database!)
Do you know of any tool that can achieve this or do I have to write it by hand?
Thanks in advance
I use EF Power Tools which is a plugin for Visual Studio.
Download here
With the plugin, you can reverse engineer your database in order to create your objects and mappings in your application. Despite the fact that it will save you a lot of time, note that it is not perfect. You might want to review your indexes and relationships as some were missing in my case.
To Reverse engineer your database, it's as simple as this:
The Reverse Engineer Code First command is used to generate the POCO,
mapping (configuration), and derived DbContext classes that are based
on an existing database.
Right click the project and select Entity Framework –> Reverse
Engineer Code First.
Enter the information about an existing database
based on which you want to reverse engineer Code First.
You can check this link from Microsoft for a complete example:
https://msdn.microsoft.com/en-us/data/jj593170.aspx
IMPORTANT: As of Entity Framework 7 (not released yet), only the Code First approach will be used. You might want to consider this before choosing another approach like Model First, for instance. You can read more about: EF7 - What Does “Code First Only” Really Mean
Open the Entity Data Model (edmx) file (edit: or create one if you don't already have one), right click on the design surface in a blank area, and select "Update Model from Database".
Select the proper connection string if prompted, then choose the "Add" tab, and drill down to the tables in your database you want to add and put a check mark by them. Click Finish and you're done.
Check out the EF power tools plugin which give you context menus for Reverse Engineer Code First as well as other code generate options
https://visualstudiogallery.msdn.microsoft.com/72a60b14-1581-4b9b-89f2-846072eff19d
Can't you just create an EDMX and only have it select the tables you want it to point to instead of the whole DB?
Look at Generate From Database in this article
https://msdn.microsoft.com/en-us/data/jj206878.aspx
I have a solution which uses Entity Framework model first approach.
The problem I am facing is that whenever I change something on a table, add a column or change a relationship,I right click and go for "Generate Database from Model", which re-generates ALL the code for the solution even if I just changed one table..and that generated code is useless for a production database since it drops every table and then re creates them..
I am wondering, isnt there be an option just to generate the T-SQL with the changes I made ? Otherwise model first would be useless after your app goes into prod.
I am using entity framework 5.0
Personally, I would suggest you to use Red-Gate SQL Compare when you need to sync your databases at Production environment.
This tool helps you to compare and synchronize databases using sync scripts without losing data (it will alert about if so) and its UI is just awesome.
I am using Entity Framework to work against a database using the database-first approach, with an EDMX file representing my database. A problem happened when I changed one property in the database, then when I erased it from the EDMX file and updated it to add it again, it shows up now without the relations to the other tables (Pk-Fk relations).
More Info:
1. tried connecting from another new project and same result.
2. tried re-creating the database and re creating the pk-fk relation, and same result.
3. tried connecting to another database with edmx, and in this case the relations were present.
4. in the sql management studio it looks like the relations are present in the tables, as well as in the diagram.
Does anyone knows what is the problem?
When I need to update a table in the edmx it normally creates another .edmx.designer file, if this is happening this could be the reason why the relations doesn't appear. Just delete the older .edmx.designer and it should work again. If this isn't the problem, sorry but I'm new to entity framework, don't know it very well
I have been updating my Entity Framework by simply right clicking and clicking on "update model from database". I usually go under the "Add" tab and then click the tables and click finish. I also use "refresh" sometimes as well. What are the differences between these? and also when I do refresh or add sometimes the entity comes out wrong or keeps some of the old information in cache, how can I just get the entity to match my database and clean out any of the old cached things.
Yes, you are right. The designer is a bit buggy and doesn't handle certain schema changes particularly well. As a rule, when I add a table to the database, I run Update model from database and select the table in the Add tab. Works fine. If I add a field to an existing table, I do Update model and Refresh. Works well too.
But if I add one field and remove another, or rename an existing field (as far as I remember), EF does not handle this correctly (added a new field but failed to remove the old one, and since the old one remained unmapped, the model validation failed). So in those more complex cases I usually delete the entity and then do Update model from database and Add it again.
The downside is that if you did make some changes (e.g. renamed some fields or navigational properties of the entity), you'll have to do those changes again.
It doesn't clean out old items. You have to delete those yourself. On the positive side, Visual studio will give you an error when you compile, stating that a coloumn or two isn't mapped. The entity framework tool is more of a code generator. It generates classes based on the structure of your database, as opposed to being tied to the database for is't structure information.
Designer is not buggy and the reason why it doesn't handle some changes is because CSDL and some MSL modifications made by user are not overwritten. CSDL is the diagram you see in designer and MSL is the mapping of your entities and associations.
Believe me this is a big step forward comparing to Linq-to-sql where no update existed and you always had to delete everything including your changes when you wanted to refresh your model. If you made a lot of changes you can always delete your entity in EF designer as well. EF designer offers a choice to update or recreate (by deleting the old one).