C＃获取具有共同属性的所有项目

Question

This should be fairly simple, but I'm having a really headache, I think I need some sleep.

I have a List from some code

The property object is like :

public class Properties {
    public int IdProperty 
    public int ProductId
}

This is much as a KeyValue pair. With example this values:

Product - Property
1          1
1          2
2          1
2          3
3          1
3          3

What I want is to get, from that list, the properties that has all products (in this case, properties with id 1)

the return list should be:

1           1
2           1
3           1

this should be really simple, isnt it ? (trying it using lambda linq)

Added tryed queries:

properties.Where(p => properties.All(x => x.IdProperty == p.IdProperty));
properties.Join(properties, p=>p.IdProperty, ... not sure what to put on other params);

some crazy 2 way lists to match.

note: I don't know the common property.

Answer 1

return properties.Where(p => p.PropertyId == 1);

Where properties is an IEnumerable<Properties> containing the property objects you want to select from.

EDIT Now understanding your question, one way to get all property ids common to all products would be:

var productCount = properties.Select(p => p.ProductId).Distinct().Count();
return properties.Where(p => properties.Count(x => x.IdProperty == p.IdProperty) == productCount);

Answer 2

I guess you don't know which property is common to all products...

// get number of products
var nbOfProducts = properties.Select(x => x.Product).Distinct().Count();

// group records by property
// and get only groups with number of items same as number of products
var result = properties.GroupBy(x => x.Property)
                       .Where(g => g.Count() == nbOfProducts)
                       .SelectMany(g => g);

Answer 3

yourCollection.Where(p => p.PropertyId == 1);

or

yourCollection.GroupBy(p => p.PropertyId);

This 2nd option will group them so that you can get other ones if you need them.