![]() ![]() Keep experimenting with Entity Framework and it will not stop surprising you. Join bs in booksSeries on left.BookSeriesId equals bs.Id into books_bookseriesįrom left2 in books_bookseries.DefaultIfEmpty() The left outer join syntax preserves the unmatched rows from the left (FactInternetSales) table. Join b in books on a.Id equals b.AuthorId into auth_books The last example will look like this with query syntax: In the current examples I use method syntax, you can change it to LINQ query syntax. You just saw how you can use GroupJoin and DefaultIfEmpty to make left joins. Resulting query is a join with three tables where Books and BookSeries tables are joined with left join. GroupJoin (books, authur => authur.Id, book => book.AuthorId, (a, b) => new )).ToList() Var books = dbContext.Set().AsQueryable() Var authurs = dbContext.Set().AsQueryable() Let’s now make a real left join query by using GroupJoin and DefaultIfEmpty().įirst example is a query to return all authors and their book. In the resulting query tables are joined with left join: Include(a => a.Book.Select(b=>b.BookSeries)).ToList() Var resList = dbContext.Set().AsQueryable() In many cases when you make queries and you load objects using entity framework’s navigation properties generated queries will use left join automatically.įor example we load all authors and include all books and their series:ĭ = s => System.Diagnostics. Librar圜ontext dbContext = new Librar圜ontext () Įnable logging so you can see the SQL queries sent to the database in your output window.ĭ = s => System.Diagnostics. Make sure that you have included the following namespaces in your code samples: When you finish with the generation you have the following classes: If you are used to the old fashioned way of generating classes from database tables, this option is for you. For the generation I use “Code first from database”. I am a fan of Microsoft SQL Management studio and I like to design my database with it first, after that I generate Entity Framework models. In the examples bellow I use a small database. One reason is because filtering operations dont require an INNER JOIN and can be done with a. From his long software development experience, he shares how to make left joins with Entity Framework. LEFT JOINs are by far the most common SQL join operation. ![]() Yavor Ivanov has been in Melon for 9 years now. ![]()
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