As a apprentice for web development, I have no clue of preventing dirty write for web forums. Is there any food for thought? Thanks in advance!
I'm working on ASP.NET MVC and Entity Framework.
Okay, sorry for misleading. The dirty write here means overwrite changes of another person in the database. While using a Optimistic Concurrency.
To do optimistic concurrency in the EF, you:
Add or select a field to use for optimistic concurrency control. We use a TIMESTAMP.
In the EF designer, change the ConcurrencyMode to Fixed for this property.
Serialize the "old" value of the field to a hidden field on the form.
Deserialize the "old" value when the form is submitted, and add it to the entity you're updating.
The EF will throw OptimisticConcurrencyException when the stored value doesn't match the old value during an update.
Related
I am sorry if I am asking something that has an obvious answer, but I have spent and entire day searching for resources on the subject and I fail to find or understand how to do a few basic thing with EF7.
So, here is my question.
I have an ASP MVC 5 (VNEXT) website and I am using Entity Framework 7. I have an existing database, thus I am working database-first.
So far everything was fine. I installed everything required to get my DNX EF commands up and working; I scaffolded a dbContext and I got all my tables as classes and a dbContext class.
Everything fine, all well. I was happy and continuing with my work.
However, I got to a point where I wanted to make a property of one of the generated (table) classes Required, because I use jQuery unobtrusive validation.
I have the following resource as a reference: http://ef.readthedocs.org/en/latest/modeling/required-optional.html
My first wonder is, according to this source, in the FluentAPI the property has been marked as .IsRequired(). I believe, making it required here is a whole other thing that has nothing to do with unobtrusive validation. So, the next thing explained is simply - go to your class and add the Required data annotation.
This is all fine and well, and after adding it, it works as it should.
But I immediately wondered - well, I am modifying the generated classes, am I not going to lose those changes once I update the model?
Which leads me to my final problem - I searched for a long time, I even played with the help menu of DNX EF, but I am unable to find the right way to update the dbContext and generated models after I make changes to the database.
I believed this to be something quite trivial but to my surprise I am unable to find a resource explaining how to do the update.
Can you point me in the right direction, and tell me how to update EF generated models and context after I make changes in the database schema, and what is the best way to add annotations to the properties of the generated classes?
The general consensus is that you shouldn't use your database entities as input from users directly. Instead, use ViewModels, verify those against your validation rules, then map them to database transactions.
As asp.net MVC developer I use database first and updating database is a big head ache so I use Metadata approach and create ViewModels which helps allot.
I need to work out how to do CRUD stuff in an MVC application, passed to me by a former colleague (I don't have any other info, just the application and the database). So I can see there is Model1.edmx and the model browser that contains MyApp.Model>EntityTypes>MyTable representation, and MyAppModel.Store that contains a representation of the table, and the Model1.Designer.cs file which has methods that look like they must be CRUD related (e.g. OnLastNameChanging, OnLastNameChanged). I can run the application and insert and update records to a db table.
What I need to know is where / how do I code other CRUD operations and use Entity Framework to work with WHERE clauses, and do stuff like update another record in a table depending on the value of a given field in the record being inserted or updated.
I've worked with MVC on one other small project but haven't really worked with entities. I'm used to the WebForms / ADO.NET / stored procedures way of doing things.
Any help gratefully received.
Happy new year!
I guess you are using database first approach.
some useful links for Code first approach:
http://www.codeproject.com/Tips/793159/Code-First-Approach-in-Entity-Framework-using-Data
other for database first approach
http://www.aspdotnet-pools.com/2014/08/insert-update-delete-operation-in.html
http://www.asp.net/mvc/overview/getting-started/getting-started-with-ef-using-mvc/implementing-basic-crud-functionality-with-the-entity-framework-in-asp-net-mvc-application
I am using MVC3, ASP.NET 4.5, C#, MSSQL.
I need to create ViewModels from my Domain Model that is automatically generated by Entity Developer.
Once I create the relevant ViewModel for an entity I can comment out non required properties for a particular View.
However there is the ongoing concern that once an entity is upgraded then the ViewModel could become out of sync, and I want to minimise the risk/effort in fixing this.
Thanks in advance.
I see the same complaint endlessly about using view models. True, they can be repetitive in nature, but copy and paste works beautifully there. If you so wanted, you could even design an interface that both your model and view model must implement, which can help you keep the two in sync somewhat. However, I think you'll find that the two will diverge more than you think.
As far as validation goes, this is also a common complaint, but it's actually a symptom of bad design. Your entity class should only have validation specific to the database, which you'll find is actually pretty sparse. Entity Framework actually does a fantastic job translating most of the properties inherent limitations to the database. For example, a DateTime property's column is set as NOT NULL by default, because the C# type itself cannot be null. There's no need to add something like [Required], because the behavior is inherent.
Other types of validations such as regex are totally inappropriate for a domain model because there's no correlation to anything happening at the database level. It's entirely for the UI, and thus belongs on your view model. I think you'll find that if you evaluate all the things you're trying to validate on your domain model, you'll find most if not all should be strictly on your view model(s) instead.
I want to develop an ASP.Net MVC application with EF4 Model First design and only generate the actual database much later, ideally at the end of the project.
Based on some of the ideas here:
http://elegantcode.com/2009/12/15/entity-framework-ef4-generic-repository-and-unit-of-work-prototype/
I want to create something like an InMemoryObjectContext for testing and development and use IOC to switch to the SQL Server implamentation (EF generated) for UAT and production.
Is this wise?
Is it possible? If so, does anyone have any suggestions?
Does EF always need an underlying database in order to track changes, commit etc?
I've tried creating a model first but as soon as I add properties I get the following errors:
Error 2062: No mapping specified for instances of the EntitySet and AssociationSet in the EntityContainer Model1Container.
and the warning:
Running transformation: Please overwrite the replacement token '$edmxInputFile$' with the actual name of the .edmx file you would like to generate from.
The error doesn't stop the application running but worries me. I'm very very new to EF so I apologize if this is way off the mark or a dumb question. I'm hoping to get some good advice while I sit for the next few days and watch videos and read articles.
Thanks
Davy
At the very least you need mapping information "filled in". You can fill these fields with nonsense if you don't want to work against the underlying database.
If your doing Model first, right click on the designer canvas and select, "Generate Database from Model". This will automatically create convention based mappings for you without defining tables and columns. You don't even need a valid db connection to do this.
I'm using asp.net mvc, linq2sql, iis7 and sqlserver express 2008.
I get these intermittent server errors, primary key conflicts on insertion. I'm using a different setup on my development computer so I can't debug. After a while they go away. Restarting iis helps. I'm getting the feeling there is cache somewhere that I'm not aware of. Can somebody help me sort out these errors?
Cannot insert duplicate key row in object 'dbo.EnquiryType' with unique index 'IX_EnquiryType'.
Edits regarding Venemos answer
Is it possible that another application is also accessing the same database simultaneously?
Yes there is, but not this particular table and no inserts or updates. There is one other table with which I experience the same problem but it has to do with a different part of the model.
How often an in what context do you create a new DataContext instance?
Only once, using the singleton pattern.
Are the primary keys generated by the database or by the application?
Database.
Which version of ASP.NET MVC and which version of .NET are you using?
RC2 and 3.5.
Two guesses for you:
1) If you've got a singleton DataContext, wouldn't that mean it's shared by all threads?
The MSDN reference for DataContext says an instance is "designed to last for one unit of work" and typically created "at method scope or as a member of short-lived classes".
I'd try moving away from the singleton pattern and creating a new context each time it is needed.
2) When you say your keys are generated by the database, is that through Identity fields, or some kind of "select max + 1" pattern? If not by an identity, then you may have concurrent connections obtaining the same "next" key value. Check your transaction isolation levels.
EDIT - following on from comment
Are you sure that the index violation is on the primary key? Using SQL Server Management Studio, primary keys are normally given a PK_ prefix, and IX_ is used for further indexes. Check the fields which go to make up "IX_EnquiryType" and ensure it's not just a rare logic problem that's causing your problems.
Well, it can be because of many reasons. I'll give you some questions. Please edit your question with the info about these, and it will be much more straightforward for us to help you.
Is it possible that another application is also accessing the same database simultaneously?
This would be the most likely reason. I experienced this, too.
How often an in what context do you create a new DataContext instance?
The best way would be to create a new one per request.
Are the primary keys generated by the database or by the application?
Which version of ASP.NET MVC and which version of .NET are you using?