I guess that EF4.1 is recent to EF4.0, but I didn't find any book on EF4.1, but 2 books on EF4.0.
can I still buy the book on EF4.0 expecting that I will get most of the concept??
Thanks for helping.
According to The ADO.NET Team blog, there are two main features:
The DbContext API is a simplified abstraction over ObjectContext and a number of other types that were included in previous releases of the ADO.NET Entity Framework. The DbContext API surface is optimized for common tasks and coding patterns. DbContext can be used with Database First, Model First and Code First development.
Code First is a new development pattern for the ADO.NET Entity Framework and provides an alternative to the existing Database First and Model First patterns. Code First is focused around defining your model using C#/VB.NET classes, these classes can then be mapped to an existing database or be used to generate a database schema. Additional configuration can be supplied using Data Annotations or via a fluent API.
EF 4.0 books are good unless you are using one of those 2 features, because you won't find them in there.
But you have plenty of resources online about those new features (especially Code First).
You even have official tutorials:
Using DbContext
Code First walkthrough
Related
I am new to the ADO .NET technologies. I know EF6 is built on top of ADO .NET. I checked out some of Microsoft's Data technologies reference site (http://msdn.microsoft.com/en-us/data/).
I am trying to figure out if a CodeFirst created database that is modified after initial creation can be modified and migrated without loss of data. One of the tutorial videos on their site says DatabaseFirst EF mappings created with the entity designer cannot be migrated without loss of data after a change is made to the schema.
Do migrations for changes to schemas based on CodeFirst designs also suffer from that problem of data loss after migration?
This is good article you should read:
http://www.asp.net/mvc/overview/getting-started/getting-started-with-ef-using-mvc/migrations-and-deployment-with-the-entity-framework-in-an-asp-net-mvc-application
In the deployment section you saw the MigrateDatabaseToLatestVersion
initializer being used. Code First also provides other initializers,
including CreateDatabaseIfNotExists (the default),
DropCreateDatabaseIfModelChanges (which you used earlier) and
DropCreateDatabaseAlways. The DropCreateAlways initializer can be
useful for setting up conditions for unit tests. You can also write
your own initializers, and you can call an initializer explicitly if
you don't want to wait until the application reads from or writes to
the database. At the time this tutorial is being written in November,
2013, you can only use the Create and DropCreate initializers before
you enable migrations. The Entity Framework team is working on making
these initializers usable with migrations as well.
For more information about initializers, see Understanding Database
Initializers in Entity Framework Code First and chapter 6 of the book
Programming Entity Framework: Code First by Julie Lerman and Rowan
Miller.
quoted from that article.
I have started working on a new project and am switching from LinqToSQL to EF 4.1 as my ORM.
I already have a database set up to work with and so am going with the database first approach. By default the EF generates a context which extends ObjectContext. I wanted to know if a good approach would be to replace it with DbContext.
Most of the available examples deal with only Code First and DbContextbut DBContext can be used with Database First too. Are there any advantages I get by using the DBContext? From what I have read the DBContext is a simplified version of the ObjectContext and makes it easier to work with. Are there any other advantages or disadvantages?
You will not replace anything manually. You will need DbContext T4 Generator available at VS Gallery. Don't touch your autogenerated files - your changes will be lost every time you modify EDMX file.
I answered similar question last year. Now my answer is mostly - for new users DbContext API is probably better. DbContext API is simplified - both in terms of usage and features but you can still get ObjectContext from DbContext and use features available only in ObjectContext API. On the other hand DbContext API has some additional performance impact and additional layer of bugs. In simple project you will probably not find any disadvantage in DbContext API - you will not see performance impact, you will not use corner features available only in ObjectContext and you will not be affected by occasional bugs.
A lot of information and blog posts was collected since DbContext API was released so you don't have to be afraid that you will not find description of the API. Also ADO.NET team now uses DbContext API as their flag ship.
I'm not a big fan of DbContext API but my opinion is not related to its functionality but to its existence - there is no need to have two APIs and split development capacity of ADO.NET team to maintain and fix two APIs doing the same. It only means that there is less capacity for implementation of really new features.
I'm using it now with Oracle on an add on to an existing application. The simplification that Ladislav refers to works well for me on this project as I am short on time and resources. I have not found any gotchas as long as you stick to simple CRUD operations and less than ~150 tables.
You can still use metadata annotations to provide basic validation and localization and there is enough documentation out there but you won't find much on official Microsoft sites.
Is there a template or tool to generate code from the database directly? I want to use model first scenario but do not want .edmx file for mappings. There is a database with many tables and I do not want to write all the classes (I am lazy) for that. So, is there a template to generate the code and set the annotations/use fluent api for defining the relationships, etc automatically from the existing database?
This would be helpful in the following scenario as well. Say, I was using .edmx with POCOs and now I do not want the mappings in the .edmx file. I want the mappings in the code. It would be great to have a tool or a template to generate the mappings in the code from the existing database.
I am starting on learning EF 4.1. I think "Code first becomes model first in version 2 i.e. after the database is created/released (in version 1) and needs some changes". Is that really true? I'd love to hear some comments. Thanks.
Check out the 'Reverse Engineer Code First' feature of the EF Power Tools CTP1 that was just released.
For generating classes, you can use POCO t4 template generation. Have a look at this detailed link which will help you getting started. That way you will get all the classes generated.
For mapping, you can use Code-Only style for Entity Framework but generating classes and context using POCO template will have far more advantage over creating the mapping yourself. Imagine adding new tables or modifying the tables, it will involve more work. But I will certainly love to know if there is any mapping tool for that.
It is possible that you are using EF-provider Devart dotConnect for Oracle when working with Oracle database. In this case the following information will help you to choose the tool.
The first version of Entity Framework Power Tools also contained the capability of generating a Code-First model with fluent mapping from an existing database. Although useful, this functionality is limited as regards its flexibility: the developer can only set the connection string; following that, classes are generated from all database objects available to the user. That is not extremely convenient, since in Oracle, for example, numerous schemas containing hundreds and sometimes thousands of tables are available to the user.
Rather than resort to this limited functionality, the users of Devart ADO.NET providers can avail themselves of impressively robust design-time development capabilities of Entity Developer, an EF-designer delivered with Devart providers. Also possible is the choice between the Database-First approach, as provided in EF Power Tools, and the Model-First approach, within which Code-First classes are created in the EDM-designer.
When compared to EF Power Tools, the Database-First approach to the development of EF Code-First models also allows selecting objects that must be available in the model, setting naming rules for the generation of class names and properties and so on. Besides, the resulting model can be modified and improved in the designer.
To better meet developers' needs, Code-First code generation in Entity Developer both for C# and VB is based on the T4-template that is easily accessible and can be modified in feature-rich T4 Editor contained in Entity Developer.
For more information on Code-First development in Entity Developer, see "Entity Developer – EF Code First DbContext Template"
http://www.devart.com/blogs/dotconnect/index.php/entity-developer-ef-code-first-dbcontext-template.html
I am about to start implementing the data access infrastructure of a project that was architected with an approach to DDD (it's my first attempt on DDD, so be gentle ;-) ).
I will be using Entity Framework. Until now, I was looking into the method teached by Julie Lerman on her great book, Programming Entity Framework, where ADO.NET POCO Entity Generator is used, with some changes to the T4 templates and some more custom code.
Today I started reading articles on EF4.1 and the ADO.NET DbContext Generator, using Database First approach, and I'm trying to decide with which one should I go.
DbContext and EF4.1's approach on DDD seems to be a nice, cleaner way than POCO Entities, but I'm afraid that it could lead to some issues in the near future, since EF4.1 is still in RC.
From ADO.NET team blog, I know that EF4.1 does not include:
Enum support
Spatial data type support
Stored Procedure support in Code First
Migration support in Code First
Customizable conventions in Code First
From my understanding, since I will be using Database First there is a smaller number of features that were not included.
In conclusion, my question is:
Can I replace POCO Entities Generator with EF4.1 DbContext Generator?
From a point of view of clean creation of POCO entities, there is no difference between the two generators. Both generators produce the same entities, however, ADO.NET POCO Entity Generator is based on ObjectContext's API, whereas ADO.NET DbContext Generator is based on DbContext's API.
DbContext's API has a few very nice new features (Local, Query on navigation property, etc.) and API is somehow simplified but at the same time it looks like some features used in ObjectContext API are missing in DbContext API (or at least it has not been explored enough yet).
EF 4.1 RC is go-live release. It means that you can build a real application with it because API will not change in RTW (only bugs will be fixed). Also RTW should be in the next month so I think you will not be ready with your application before the final version is shipped.
ObjectContext API or DbContext API? ObjectContext API is much better covered by documentation and blog posts. You can find plenty of examples about it. Also its limitations are already well known. DbContext API is new release. A very promising release, mostly because of the code-first approach. There is still a very limited number of blog posts, no book and the API is not proven enough. So it depends if you are ready to fight with new API? If not, then ObjectContext API is still a good choice because you don't need the code-first approach.
I'm having a look at Entity Framework and everything I'm reading takes a data centric approach to explaining EF. By that I mean that the fundamental relationships of the system are first defined in the database and objects are generated that reflect those relationships.
Examples
Quickstart (Entity Framework)
Using Entity Framework entities as business objects?
The EF documentation implies that it's not necessary to start from the database layer, e.g.
Developers can work with a consistent
application object model that can be
mapped to various storage schemas
When designing a new system (simplified version), I tend to first create a class model, then generate business objects from the model, code business layer stuff that can't be generated, and then worry about persistence (or rather work with a DBA and let him worry about the most efficient persistence strategy). That object centric approach is well supported by ORM technologies such as (n)Hibernate.
Is there a reasonable path to an object centric approach with EF? Will I be swimming upstream going that route? Any good starting points?
Model First approach seems to be what you need.
We suggest to take a look at the ADO.NET Team Blog article also.
A while after asking this, I discovered that EF 4 supports POCO (Plain Old CLR Objects), allowing an object-centric design with (relative) ignorance of persistence.
This article was the best one I came across discussing that approach, while this article explains how to use code generation templates to ease the work.