I'm using DefiningQuery to specify a Read only "view" entity that contains fields from two tables, and it works great for my need.
But each time I'm updating my model (using the Model designer) and runs the "Generate Database from Model..." operation, my DefiningQuery is lost because the .edmx file is getting overwritten.
The SQL being generated (in the .edmx.sql file) now assumes my Read Only entity must have a corresponding table created.
Is there a way to avoid the DefiningQuery being overwritten when the model is updated?
If possible I would like to avoid having to generate a Database View and map to that.
A little info:
I'm working on a project based on the Entity Framework 6.x.
I'm using the Model First approach.
The database is an SQL Server.
Related
I have reverse engineered our model from an existing database using EF Core Scaffold-DbContext. Since then a couple of tables have been added to the database within SSMS and I now need to update the model. How can I do this without overwriting the original model classes (changes have been made to them)?
You should not make changes to the generated code, they are generated as partial classes, so you can make another file with your changes, and then simply re-generate the files.
I'm using an existing database and I have mapped one of the tables as an entity (as i needed to map a foreign key).
So when it comes to initialising this database I would like EF to ignore this entity since it already exists.
How would I go about doing this?
You should create an empty migration as the first migration with the -IgnoreChanges flag to allow Entity Framework to get a snapshot of the existing database.
So out of the gate use:
Add-Migration InitialMigration -IgnoreChanges
and that will create a blank migration but it will update the Entity Framework metadata allowing the existing tables to exist and not be touched by migrations.
Also to be mentioned that the naming conventions that Entity Framework expects and your database schema may differ. You may need to manually setup the foreign keys using the Fluent API.
I didnt check with EF 6 specifically, but I think default EF behavious is that when the database exists, then it presume all model be ready and therefore will create no tables. If you want your initialization code to create tables with code first, use initialization code for prepare data. Look here :
http://www.entityframeworktutorial.net/code-first/seed-database-in-code-first.aspx
I've been using EF for a while (4 with model first) and so far I've not created any mapping manually. Whenever I need more entities/tables, I add an entity and the associations (all foreign key) and click "update database from model", which, as is well known, doesn't update any database from the model (although it does need a database connection for reasons I don't know). What it does is generating a storage model and the appropriate mappings to it, which are all stored back to the same edmx xml file.
So far, that has always been enough for me but I'm wondering what the workflow would be if one is to tweak the mappings and storage model manually. "Update database from model" overwrites all manual customization - so how is one to fix most of the mappings and storage model? Because I clearly don't want to do it all by hand - in fact I couldn't even figure out how to actually create a table in the storage model other than by editing the edmx in the xml.
I have the same problem. I just use a mixture of methods. If I add a field to the database, I just add the field to the model file. If I do a major restructure, I delete the table and recreate it by generating it from the database. Sometimes, I actually edit the edmx as XML to change or add things. You just kinda gotta figure out what process works best for you. I have managed to avoid heavy customization in the edmx by using the T4 template or changing the database and regenerating.
Trying to understand Entity Framework. My approach is database first. However I would like to define other entites in the model that is closer to my business objects. I guess I could write queries in the db and include them in the model. But I would also like to define entirely new entities in the model though they would be based on underlying tables in the db. How do I do that - does anyone know a tutorial?
Regards
Bjørn
db Oldtimer, EF Newbie
Database first means that you have existing database and you can either create model by updating from database or manually. You can use wizard to create initial model and modify it manually to define new entities but you must not use update from database any more or some of your changes will be deleted. Also your custom modifications must follow EF mapping rules (for example it is not directly possible to map multiple entities to the same table except some more advanced mapping scenarios like splitting and inheritance) and some of them (custom queries) must be done directly in EDMX source (XML) because designer doesn't support them - this requires more complex knowledge of EF mapping and it will be definitely hard for newbie.
You can check specification of that XML. For entities mapped to custom queries you will have to use DefiningQuery element in SSDL part of EDMX.
I see that EF can update a model based on an existing database schema. However, I'm starting totally from scratch; I don't want to build tables, then rebuild them in the EF model file. Is there a way that I can draw out a model file, and have the SQL tables automatically be created for me?
Unfortunately, you have to wait for version 2 of EF.
Here is a link to the EF team's blog, where they talk about adding Model First support in v2:
One of the most painful omissions from the Entity Framework V1 was Model First, which basically means creating a conceptual 'model first' and then deriving a storage model, database and mappings from that.
[...]
The next release of the Entity Framework will include the ability to generate database schemas from your model. The main entry point into this feature is via the Designer context menu, to which we will add a new option called “Create Database from Model”.