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![]() ![]() i first used the correct version of EF and then reproduced your problem before adding the correcting code. You can also just load the existing instance into the changetracker but this incurs a roundtrip to the db and will attract some SO critics to the party.ī.t.w. Right-click on the Model folder and proceed as shown in the following screenshot: Choose 'Visual C' > 'ADO.NET Entity Data Model' then provide the name as you need to (for exampleNorthwind.edmx) as in the following: Click 'Add' then a new window will appear as in the following: Select 'Generate from database' and click 'Next' the. The solution is to first attach a shallow copy of the blog instance (without a populated collection of posts) and then add the new posts. Contains method to generate an IN clause rather than using a join. Alternatively, if you know that the number of records on one side of your query are relatively low (under 2000) you could get the IDs from the first table and then use the. Here, you will learn the new features of querying introduced in Entity. You could add a linked table in one database and then join it. ![]() Visit the LINQ-to-Entities chapter to learn more about the basics of querying in Entity Framework. Your problem is that when attaching the blog instance it contains an collection of new and existing posts. Querying in Entity Framework Core remains the same as in EF 6.x, with more optimized SQL queries and the ability to include C/VB.NET functions into LINQ-to-Entities queries. How do you attach entities to a db context and set their state correctly. I understand the question now, me thinks. No one else knows the `post` object directly. Using (BloggingContext db = new BloggingContext())īlog = db.Blogs.Include("Posts").Single() Sometimes, a query in one form translates to the server but if written in a different form doesnt translate even if the result is the same. Not all LINQ operators have suitable translations on the server side. This feature allows the same context instance to dynamically connect to different databases. Also, the connection or connection string can now be mutated on the context instance. However, loading and saving happens in different contexts and I modify it by adding another object to a collection property of the object.Ĭonsider the following code based on the famous blog/posts example from MSDN: Blog blog Language Integrated Query (LINQ) contains many complex operators, which combine multiple data sources or does complex processing. In EF Core 5.0 new features, It is now easier to create a DbContext instance without any connection or connection string. The context class manages the entity objects during run time, which includes populating objects with data from a database, change tracking, and persisting data to the database. Defining a DbContext derived class The recommended way to work with context is to define a class that derives from DbContext and exposes DbSet properties that represent collections of the specified entities in the context. With the Entity Framework (EF) I want to load an object from my database, modify it and save it back. Bind objects in memory to UI controls This page gives some guidance on how to manage the context class. ![]()
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