I'm following an MSDN article on applying the Repository Pattern and the Unit Of Work Pattern to Entity Framework, but I'm stuck at the mapping between the custom-made domain models and the as-yet-nonexistant database.
The article has me create two simple POCOs, Employee and TimeCard. It also walks through creating generic repositories and custom implementations therein. (I'm using the custom repositories so I can try to keep EF dependencies in the data access assembly.) However, they sort of glaze over an important step in the mapping. The article says:
With the POCOs in place we can create an Entity Data Model (EDM) in Visual Studio (see figure 1). We will not use the EDM to generate code for our entities. Instead, we want to use the entities we lovingly craft by hand. We will only use the EDM to generate our database schema and provide the metadata EF4 needs to map objects into the database.
The "Figure 1" it references is here:
But that's all it says on the subject. There's an aside on how to generate POCOs from an EDMX. There's lots of information via Google on how to generate POCOs, generate EDMX from a database, etc. But in this walk-through we already have the POCOs and I need to use them in the EDMX which would, in turn, generate the database (I'm assuming, based on other code-first walk-throughs).
I've added an "ADO.NET Entity Data Model" to the project, which is basically a blank canvas. But I'm not seeing how to add my existing POCOs to that canvas. Do I have to re-create them manually on the design surface (which would be a pretty significant duplication problem in a larger domain)? If so, how do they map to the existing ones?
Typically when you use the designer the flow is the opposite - you create the model with the designer (or create/update the model from the database) and then the code is created for you. The created code can be either the EF1 style code with entities derived from EntityObject and attributes etc. which is created with a Single File Generator which is a part of VS (Code Generation Strategy set to "Default") or the code can be created with T4 templates (Code Generation Strategy set to "None") in which case you need to add T4 templates to your project. EF matches POCOs with Entities from the edmx file by convention (names of entities have to be the same, names and types of properties have to match etc.). In the article for some reason they went the opposite way which is weird since it requires that you create all the entities and relationships with the designer manually (since the designer does not know how to create entities from the code) and make sure that the requirements for the conventions (you may not even be aware of some of them) are met. However when you start with code the better approach is to use the EF Code First approach and skip the designer entirely. Code First can create database from your code. It also contains migrations feature which allows evolving your database along with your code. Finally (as you seem to use Visual Studio 2010) you could use EF6 which allows using all the goodness that was previously only available on .NET Framework 4.5 to be used on .NET Framework 4. See here for more details: http://entityframework.codeplex.com/
*the names are going to change in the new version designer that supports EF6 and works with Visual Studio 2012 and Visual Studio 2013
EDIT to address questions from the comment
If you would like to use Code First would use the DbContext API which is a streamlined wrapper of the ObjectContext API. Here is a walkthrough that should help get you started.
You can still use Code First if you have an existing database - the difference is that you will not be able to use migrations. The easiest way to get started with this is to use EF Power Tools. Take a look at this tutorial to see how to do that.
More help here
Related
I currently use EF6 and use the model first approach. As I understand it, EF7 will be moving away from using an EDMX, and going from a more code-first approach. Now I know I will still be able to reverse engineer from my database into classes if need be.
However one thing I am not sure about is any manipulation I currently do with EF6 will be supported in anyway in EF7.
At the moment, I write T4 templates that read through the EDMX, pick up on the entities, and create new classes based on them. For example, I create partial classes for each entity that has deep clone methods in them. I also create repository classes based on the entities and create methods for finding by primary key, based on which properties in each class have been identified as the primary key.
If I lose the EDMX, does this mean I need to go back to manually creating these? Or is there another way?
If you want to keep using T4 templates, you can switch to something like CodeFirst -> ReverseEngeneer approach.
You update model in code, generate new migration, test it on a database and then use a reverse engeneer code first approach (http://msdn.microsoft.com/en-US/en-en/data/jj593170.aspx) to generate everything else. Theoretically it can be automated.
In my team we do it manually, but we do not need migrations, only a code first contexts and a lot of additional things, that T4 generates whery well.
Yes, you can still use T4 templates with Code First, We navigate Entity Classes instead of the EDMX Model, .
I have been looking at VS2015 recently and having some issues with T4 and asp.net 5 and related projects (FileManager hangs for multiple file outputs and you will need the latest version of Visual Studio, currently Update 1)
We are starting a new large corporate project. The database will be 100+ tables and we will be using Entity Framework, Web API and MVC.
My question is specifically related to the Entity Framework aspects of the solution.
I am trying to make a choice between the following:
Code first to an existing Database
EF Designer to an Existing Database (Database First)
I know we can use EF to generate the database from code first or from the EF designer, but we prefer to have full control over the database and develop that in the traditional way, so we have excluded the EF options that allow us to auto-generate the database.
Most of what I can find on the internet relating to Code First deals with creating a new database and then using code migrations. And when the discussions deal with Database first then the discussions favour the EF Designer. Example here: Code-first vs Model/Database-first
My preference is to go with the combination of Code First to an existing database.
The following are my considerations for favouring this option and I'm wondering if there is anything else I need to consider, and whether my assumptions/thoughts are correct.
Code first to an Existing database
There will be a large number of classes to construct at the start, but we could do the initial generation from the EF Model Wizard.
The classes could then modified with any custom properties or to remove anything we don't need, rather than the EF Designer that would require us to extend any classes.
The disadvantage is that any changes to the database would have to be manually added to our classes, unlike using the designer which will allow easy updating.
Edit:
I think I was confused in this area. From reading, it appears that the correct way to do Data First is to create partial classes for all the auto generated classes, and then to make any modifications to the partial classes as part of the 'business' layer.
My thought has therefore changed from favouring the Code First from Database, to using the EF Designer to existing database and then creating the partial classes.
In any case you'll have to synchronize the EDM (entity data model) and the DB. You have to make sure that the EDM is fully compatible with your database. If not, it will fail, no matter if it's Code First or you use a Model.
The only difference is that:
using the designer you can do it graphically, and easyly set properties, column names, and so on
using Code First, you have to set these properties, columns names, data types and so on using conventions, Fluent API or attributes
With Code First the only advantage is that once you've synchronized the Code First model (see "Code First is also an EDM, but somewhat limited") and the database, you can start using Migrations, and evolve your model using them, which later makes it easier to apply changes to the production DB (whenever a new version is released). With graphic model you cannot use migrations, and have to upgrade the Db directly from Visual Studio, or creating SQL DDL scripts by hand.
Code First is also an EDM, but with a few missing functionalities
It doesn't matter if you use Code First or draw a model, an EDM (entity data model) will be generated. If you're used to design databases, probably you'll be more comfortable using the designer. Beware of the notes on EF Core (former EF7) below!.
However, the EDM generated by Code First has a few limitations that the designer doesn't have.
The most outstanding limitations of Code First is that in the designer you can easily map user defined functions from the BD, for example scalar and table value functions, and stored procedures. With Code First there are much more limitations.
in EF 6.1 most of this limitations dissapear, but it's still a bit difficult to make the mappings.(In fact, as of today, 2014, there's only a sample, and a simple Nuget package on how to do it.).
As of march 2017, non-Core EF, i.e. EF 6.1, is no longer being updated. MS will probably solve bugs if they appear, (this was wrong: but don't expect further changes)
New features appeared in 6.2: What's new in EF 6.2, which includes definition of indices with Fluent API, support for Like, support for non-identity DB generated keys, like SEQUENCE and some other changes
Changes on EF Core, former EF7 (as of may 2015)
At this time Microsoft is developing EF 7, but it's also maintaining EF 6.x. The current recommendation is to keep using EF 6 for some time, because EF 7 is not mature enough.
EF 7 is being developed from scratch to overcome the inherited ObjectContext which was posing terrible limitations to implemente new features. But it implements the most widely used DbContext with little changes. So, if you use DbContext you'll have an easy migraiton path to incoming new versions of EF.
However there is a very important change: in EF Core (former EF7) the EDM model dissapears in favor of Code First models. So, if you want to use the technology of today and assure an easy upgrade to new versions, don't use Model First or Database First: use Code First. There are important reasons for Microsoft to have taken this decision: Code First works much better in a team environmet with version control, and allows to work with Migrations. Anyway tou can still see the model in a graphical way (with Power Toools) or use a third party tool to create the model using a designer (several of the current commercial solutions will support this for EF7).
NOTE: Why is much better Code First in team environments? If several team members modify the model it's much easier to merge changes in several code files, than in a big XML file, with lots of lines which defines the model. It's also much harder to understand the changes between versions in this hugh XML file. For medium or big projects, I recommend you to move to Code First ASAP
Is it possible to auto generate the POCO classes and the mapping with the database defined separately using Fluent API (instead of annotations) for an existing database? Instead of coding all these entity classes manually, I find it easier if they are auto generated and then I can change them as required if the names are not incorrect (plural or singular) or the some of the relationships are not correctly mapped etc. This will save lot of time for me compared to coding all the entity classes and relationships from scratch and I am not that familiar with the fluent API syntax as well.
Yes, i encourage you to use Entity Framework Power Tools CTP1
Reverse Engineer Code First - Generates POCO classes, derived DbContext and Code First mapping for an existing database.
hope this helps
The Power tools are incredibly slow to generate files. It takes over an hour to work on my companies database (has a lot of tables).
Instead take a look at this visual studio extension http://visualstudiogallery.msdn.microsoft.com/ee4fcff9-0c4c-4179-afd9-7a2fb90f5838
It generates cleaner code, WCF serialisation classes, and includes the database default constraints as part of the POCO ctor.
Disclaimer: I should mention that I am the author of this extension
We are about to start using EF as our ORM. We have our own MetaData representing the databse stracture and we will generate whatever we need off of that.
We are wondering whether to use the "old" EDMX approace, or to use the new EDMX free approach (wiht DbSet and DbContext). As we do our own code/edmx generation it seems odd to generate an EDMX and then generate objects and context off of it.
The thing is I don't see much talk about about the EDMX free approach. Is it being used by anyone? Can someone with experience share their impressions? Are there known limitations? Are there pros and cons?
Asher
Are you asking if anybody is using code-first? :) By checking the number of questions in entity-framework-4.1 and code-first and ef-code-first I guess people are using it a lot. There were several questions about code-first x non code-first. Some of I answered:
EF POCO code only VS EF POCO with Entity Data Model
EF Model First or Code First Approach?
EF 4.1 Code-first vs Model/Database-first
Generally there are four approaches:
Model first (database generated from EDMX)
Database first (EDMX generated from database)
Code first (database generated from code mapping)
Database first with code mapping (code mapping manually created for existing database or manually updated mapping generated by EF Power Tools CTP)
Selection of the approach usually depends on the way how you want to develop application (as described in linked answers). It also depends if you want to use ObjectContext API or DbContext API. The former one is usually used with first two approaches (but the secret is it should work with code-first as well) the later one with all of them.
Code first has some limitations - it doesn't support all mapping features EDMX does for example:
Stored procedures mapping (it doesn't mean you cannot execute SP when using code first)
SQL functions mapping
Advanced EDMX features like defining queries, query views, model defined functions
etc.
What I don't understand is why are you trying to combine your code generation tool with EF. Either use your stuff or use EF's stuff. You will avoid complications and incompatibilities.
I am writing my first WPF and EF application. I am using SQL CE database and I have added few tables to the DB. The EF diagram is generated and now I want to generate the classes. I am new to EF and MVVM both.
When I right-click on a Table diagram, it gives option "Add Code Generation Item..". On selecting it, there are two options:
Add Entity Object Generator
Add Self-Tracking Entity Object Generator
I want to know what is the difference between the two. Which one should I use? I also want to know which one is latest and what is POCO?
A POCO is a Plain Old CLR Object... a simple class that has only properties.
http://en.wikipedia.org/wiki/Plain_Old_CLR_Object
There are 3 approaches that the Entity Framework delivers.
Model first (you create a model in visual studio and generate the database)
Database first (thats what you do, you generate a model from a existing database)
Code first (the newest one, you just write you POCOS and the entity framework generates the database)
I think it is enough to generate the diagram from database. The context and models should be available after this.
Neither of those is the POCO generator. The best way to get that is to install Entity Framework 4.1. You'll then see some new options in the list to add a code generation item.
I'm a pretty big fan of the DbContext/POCO generator added in 4.1 as the code it creates is VERY easy to work with compared to the older stuff, and it works well in a DB First setup like you're using (which is also what I use).
You can give this code generator a try:
http://salardbcodegenerator.codeplex.com/
It generates data annotations and implements INotifyPropertyChanged for CodeFirst approach.