comparing equality 2 lists resulting from entity framework query result in c#

Question

My code

    query1 = select value1, value2 from dbo.animal where animalname="tiger";
    query2 = select value1, value2 from dbo.animal where animalname="lion";
    List<Animal> list1 = db.ExecuteStoreQuery<Animal>(query1).ToList();
    List<Animal> list2 = db.ExecuteStoreQuery<Animal>(query2).ToList();
    // list1.Count = 1 list1[0].value1 = "a" list1[0].value2 = "b"
    // list2.Count = 1 list2[0].value1 = "a" list2[0].value2 = "b"
    // Now I would like to compare list1 and list2 to see if they are equal
    var list3 = list1.Except(list2);
   //At this point list3 is containing both list1 and list2 and using var made it
 //GenericList not the same type of list as List1 and List2

I tried List list3 = list1.Except(list2) but I get compile error.

So the question is how do I find out if list1 is equal to list2? I was hoping list3 would be the differences between list1 and list2 and therefore if the lists are equal list3.count() should be 0.

The nice thing about my data is I believe data in from query1 and query should be both in order and result in only 1 record each.

Sergey Kalinichenko · Accepted Answer · 2014-05-30 16:51:39Z

1

First of all, checking if the results of Except are empty cannot answer the "are these two lists equal?" question. It answers the "does list2 contain all the elements of list1?", which is not the same, because list2 may contain additional elements.

The nice thing about my data is I believe data in from query1 and query should be both in order and result in only 1 record each.

You can compare two identically ordered lists for equality using SequenceEqual, like this:

bool areIdentical = list1.SequenceEqual(list2);

If the ordering is different, you can also force it to be the same with OrderBy:

bool areIdentical = list1
    .OrderBy(animal=>animal.Id)
    .SequenceEqual(list2.OrderBy(animal=>animal.Id));

answered May 30, 2014 at 16:51

Sergey Kalinichenko

729k85 gold badges1.2k silver badges1.6k bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

DoodleKana Over a year ago

That is good to know. So I used SequenceEqual and for some reason areIdentical is false when list1 and list2 have exact same animal object. Do I need to implement custom Equals method for Animal type for SequenceEqual to work?

Sergey Kalinichenko Over a year ago

@DoodleKana Yes, custom GetHashCode and Equals need to be there in order for the SequenceEqual to work properly. A good news is that if Animal has an Id, you could implement both of these methods by forwarding them to Id.

DoodleKana Over a year ago

Awesome, I implemented both Equals and GetHashCode. When implementing Equals did seem very redundant. I wonder if there is shortcut if you meant to compare all the fields. My code looks like public override bool Equals(Object obj){ Animal a = (Animal)obj; if(a.name==name)&&(a.height==height)&& so on etc (20 members) return true; }

Sergey Kalinichenko Over a year ago

@DoodleKana The only shortcut I know is to use the database ID, if your Animal class has one. Otherwise, you're stuck with checking member-by-member equality. Of course you could drop the inner if, and go for return (a.name==name)&&(a.height==height)&&..., but this wouldn't shrink the code all that much.

DoodleKana Over a year ago

Unfortunately my class does not have id. But I did take your advice on just using return with no if. For the GetHashCode I used return field1.GetHashCode()*17 + field2.GetHashCode() + etc. It seems to be working. Not sure if you have to list out every field. But sounds like if you are comparing them all you would have to use all fields. I multiplied the first field by 17 cuz I saw some example on stackoverflow someone using it as a primenumber.

|

Collectives™ on Stack Overflow

comparing equality 2 lists resulting from entity framework query result in c#

1 Answer 1

6 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related