Hi, in this video, we're going to think about data objects, instantiating classes, putting those classes into collections, and then using LINQ to query the contents of those collections.

For this particular demo, we're re-using some ready-written code and I'll talk you through that now. Our starting point actually is a class called 'pet', and inside that class, we can see we defined the number of properties: ID, name, animal type, breed, year of birth, and for the first part of the demo, three other properties that are fairly significant, the name of the pet's owner, the owner's address and the owner's phone number.

I've defined also an owner class and we want to make-, create owner objects from pet objects, and what we're gonna do is pull in those last three pet properties to create a name, address, and phone number inside an owner object.

Our program logic looks like this, so we create six pet objects and add them to a pets collection, and you'll notice that the first owner of the dog, Fido, is a, a woman called Grace Hopper. She lives at 1, The High Street and she's got this phone number down here, and we can see that these other objects have been created in a similar way.

So, what we do is create a collection of owners using the owner class, and then we use LINQ to go into the pets collection, and for each pet, we are going to select a new owner object, set the owner object's properties, name, address, and phone number, equal to the pet's dot owner name, pet's owner address and the pet's owner phone number, and therefore having-, we'll, we'll have created or converted our pet object's data into a collection of owner object-, owner objects.

And we 'ForEach' around that collection down here to see the, the output. So, if I was to run that to the break point, we can see that we do print out 'Grace Hopper, 1, The High Street', with the appropriate phone number and the other data's come out as well, so we've created these owner objects from, effectively, a collection of pets.

We do the same thing down here but we're using method notation rather than query notation, so we're making use of the select method and then doing something fairly similar.

For each pet, we're creating a new owner object, setting the owner object's name, address, and phone number properties equal to the pet object's owner name, owner address, and owner phone number, and again, print out the result of that.

So, we'd expect the result set to be exactly the same, and we can see, down here, that the same data's been printed out again, including 'Grace Hopper' and that same address.

So, the next thing we're going to do is a similar thing but we're going to create pet age objects from our pets collection. Pet age object is defined like this, where we are specifying an ID, a name, and an age, and note that we want to find out what the pet's age is but in the pet class, we are storing away the year of birth.

That means we're gonna need to do a little calculation to determine how old our pets are, given the current year being 2023. If I got back to my program code therefore, we are-, create a collection of these pet age objects and we have a query notated LINQ expression, where we, again, are iterating around our pets collection and we're creating new pet age objects.

We're picking up on the ID and name directly from the pet objects and setting the pet age, ID and name properties, but when we come to set the age property, we do a calculation, where we subtract the year of birth from the current year.

That won't always be exact with respect to the pet age because it depends on where we are in 2023 as to-, and, and when the pet was born as to whether that's exactly correct but we're not that worried about that for this demo. We're really trying to highlight the fact that we can do calculations to generate values for our properties.

So, if I run that or continue to run the program to the next break point, we can see that we've created these pet age objects and we've calculated the age of Fido to be three.

If I scroll back up to the top here, we can see that Fido was born in 2020, and so therefore three is the appropriate age, and we can see, for pet, the, the, the pet called Fifi was born in 2019, and Fifi's got an age of four, which is also correct.

So, in this video, we've seen how we can use LINQ and its 'select' statement to convert from one data type to another.

Practical example of using LINQ with data objects

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