使用ac＃lambda表达式获取所有有孩子的父母

Question

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I write my posts in a text editor before I put them here and I pasted in the wrong block of text entirely.

I'm so tired I shouldn't be operating heavy machinery or keyboards.

I will mark the answer below as correct, because it certainly is.

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How would I write a lambda query for the following scenario?

All Barcodes have a Category, but not all Categories have a Barcode. 

Select all Categories that have a Barcode.

Looking for something along the lines of:

var categories = db.Categories.Where(...)

This question probably already has an answer, but I apparently lack the search terms to find it.

Thank you!

Answer 1

var categories = db.Categories.Where(category => category.Barcodes.Any())

或可能

var categories = db.Categories.Where(category => category.Barcode != null)

Answer 2

var catsWithBarCode = Categories.Where(c => c.Barcode != null);

Answer 3

From the description the relation seems to be: Category {1}---{0,1} Barcode

If the size of Categories is extremely large (it is always larger than Barcodes) the alternative will be more performant.

Barcodes.Select(c => c.Category);