entity-framework-4 | 易学教程

EF4 - Context.Entry isn't available to change an Entity State

阅读更多关于 EF4 - Context.Entry isn't available to change an Entity State

问题 I use an EDMX schema as my context. On a previous project where I didn't use a schema, I could change the entity state like this: public void SaveProduct(Product product) { if (product.ProductID == 0) context.Products.Add(product); else context.Entry(product).State = EntityState.Modified; context.SaveChanges(); } But in this project, I don't see .Entry in my intellisense (and it won't suggest a namespace reference if I just type it in). I tried to modify an entity ans save it. It worked

Performance of stored procedures & Entity Framework

阅读更多关于 Performance of stored procedures & Entity Framework

问题 Are there any obvious reasons why calling a stored procedure via my entity model would result in far slower performance than calling it direcly? Firstly, I don't expect the SP to run at exactly the same speed and I know that there are various things that EF has to do that wouldn't be called when accessing the SP directly. That aside, I have a query that returns three columns of strings. It runs pretty much instantly when I execute it via Enterprise Manager. If I run it via EF then it takes

Entity Framework 4 (CTP 5) unwisely queries in comparison with LINQ-to-SQL

阅读更多关于 Entity Framework 4 (CTP 5) unwisely queries in comparison with LINQ-to-SQL

问题 I have an issue about Entity Framework 4 CTP 5, which I realize LINQ to SQL handle it better than this, but I insist on using EF 4 because of its Code-First feature. So here is my problem: Imagine products with its Tags (or whatever with one to many relation). And tblTags will be changing by deleting some and inserting some tags at a time by user (and user might change them completely different). So in my opinion we can simply delete all old tags and insert new ones (simplest thing to do),

If you create a DomainService, exposing an entity, can you access aggregate entities?

阅读更多关于 If you create a DomainService, exposing an entity, can you access aggregate entities?

问题 Say you create an RIA DomainService and you include a Person (shown below) entity in it, can you access aggregate entities on that object? For instance, if I have entities like so (keep in mind that this is a naive representation, they are modeled via the EF4 designer): public class Person { string FirstName { get; set; } PhoneNumber { get; set; } } public class PhoneNumber { public string AreaCode { get; set; } public string Trunk { get; set; } public string Number { get; set; } } If I

How To Count Associated Entities using Where In Entity Framework

阅读更多关于 How To Count Associated Entities using Where In Entity Framework

I have this: var queryResult = (from post in posts select new { post, post.Author, post.Tags, post.Categories, Count = post.Comments.Count() }).ToList(); But I need something like this: var queryResult = (from post in posts select new { post, post.Author, post.Tags, post.Categories, Count = post.Comments.Where(x=>x.IsPublic).Count() }).ToList(); But post.Comments is a ICollection How about using Enumerable.Cast<T>() like this ? var queryResult = (from post in posts select new { post, post.Author, post.Tags, post.Categories, Count = post.Comments.Cast<Comment>() .Where(x=>x.IsPublic).Count() })

When should entity framework be used?

阅读更多关于 When should entity framework be used?

I'm new to Entity Framework and, of course, I have found few questions on SOF with regards to target use-cases. Let me give you some information. I'm not dealing with different database vendors or different databases; one, and only one, SQL Server 2008 and the database has less than 30 tables. Do I really need to redo things and go with Entity Framework? EDIT: Thanks to James for fixing my question. So I'm assuming using EF adds up overhead and does some work in background which I won't know. This is MS working style so I guess my next questions are: Does it affect performance as well? Does it

How to use Entity Framework 4.0 with Xml or in-memory Storage (non-SQL)

阅读更多关于 How to use Entity Framework 4.0 with Xml or in-memory Storage (non-SQL)

How do I specify Xml or just in-memory storge for Entity Framework models? The connection string requires a provider (usually a SQL provider string). But it won't let me omit the provider. I realize I could completely throw away the designer generated objects and go pure POCO, but then I'd have to implement my own serialization layer (could do that, but it's overkill for the tiny project I'm working on). Is there built-in support in EF 4.0 for this that I'm missing or do I just need to go the pure POCO route and discard the designer experience entirely :( Shiraz Bhaiji If you want to store

Is my understanding of POCO's + Entity Framework v4, correct?

阅读更多关于 Is my understanding of POCO's + Entity Framework v4, correct?

can someone please confirm/correct me, with my understanding of using POCO's with the Entity Framework v4? If I'm going to want to use POCO's with my EF4 context, do I still need to place/create ENTITIES on the designer/.edmx ? Isn't the idea of using POCO's so I don't need to use those 'heavy' entities? or do i still need those entities, it's just that somewhere else I actually move the data out of the entities and into my POCO's .. which is what gets used by any consuming code? If you want to use POCO you have three choices: First choice is to create EDMX model. In EDMX you will turn off

Entity Framework - IQueryable to DataTable

阅读更多关于 Entity Framework - IQueryable to DataTable

问题 I'm trying to convert an IQueryable object to a DataTable . Here's an example of a query that I would like to convert to a DataTable : var query = DbContext.SomeObjectSet.Select(x => new { PropertyName1 = x.ColumnName1, PropertyName2 = x.ColumnName2 }); Please note the anonymous object that is created in the Select method and the names of the properties: new { PropertyName1 = x.ColumnName1, PropertyName2 = x.ColumnName2 } After Googling this issue, I came across the following code that

Can we use EF migrations with MySql

阅读更多关于 Can we use EF migrations with MySql

问题 Is there a way to use EntityFramework 4.3 beta with migrations with MySql database? Can we use migrations with MySql Database? Is it possible to use incremental database development with EF code first without me touching the database 回答1: Theoretically yes. Practically you first need to get (or create yourselves) class derived from System.Data.Entity.Migrations.Sql.MigrationSqlGenerator which will be responsible for generating SQL for MySQL. Here is more about customizing (or rewriting) SQL