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Bird Search Extension11:44 with Carling Kirk
We'll write a custom extension method to implement a search feature on our Bird Watcher data set.
I saw a bird recently that I couldn't identify. 0:00 I've got some clues though. 0:03 It was blue, brown, and black, and it was medium size. 0:05 And I saw the bird in the United States. 0:09 We can build a search feature for our bird data so 0:12 that we can find out what bird it was I saw. 0:15 Think about a typical advanced search scenario. 0:18 There's probably multiple text boxes with different labels on them. 0:21 Maybe a drop down list for size that gives options for tiny, small, medium, or large. 0:25 The text boxes are for string inputs, like bird name, colors, and location. 0:31 And then there's probably a Go button to initiate the search, and 0:37 then it should return a list of birds that match the search parameters. 0:40 And probably not all of them at once, but ten at a time. 0:44 And we need to click next or previous to browse the results, and 0:47 sometimes there's an option to view more than 10, like 50 or 100. 0:51 Let's check out how we would implement that search feature using link and 0:56 our bird data. 0:59 Okay, we're back in Workspaces. 1:01 Let's create a new file called BirdSearchExtension. 1:04 New File > BirdSearchExtension.cs. 1:07 Then let's put in the namespace, which is Birdwatcher, 1:18 and we can create a new class called bird search, 1:24 Public class BirdSearch. 1:29 So it’s duty will be to hold the search data will pass into our yet 1:36 to be implemented search feature. 1:40 Let’s give it some properties. 1:42 Public string CommonName, get set. 1:44 Public List of strings for 1:50 the colors, so 1:56 list of strings, color, 1:59 get set and a string again for 2:05 Country get set. 2:11 And public string Size, 2:15 that's the size of the bird, get set. 2:19 And then our page and page size, 2:26 so we'll do a public int Page for 2:31 page number, and 2:36 a public int PageSize get set. 2:39 Okay, now, remember that the link 2:45 is just a bunch of extension methods tacked onto the i numeral interface. 2:48 We can write our own extension method to search for birds, so 2:53 we'll need a new static class in here. 2:57 Let's call it BirdSearchExtension. 3:00 Public static class, 3:03 BirdSearchExtension. 3:07 And so inside this class, our extension method will also need to be static, 3:14 so public static and let's call it search, and it'll return an i innumerable of bird. 3:20 IEnumerable of Bird, and 3:28 Search for the name of the method. 3:31 So now, since this is an extension method, the first parameter will be the object 3:37 from which it's called, which is also going to be an IEnumerable of bird. 3:42 And we need to use the this modifier to indicate that it's an extension method, 3:47 this IEnumerable of Bird. 3:51 And we'll call it source if you remember from the documentation, 4:00 that's how Microsoft did it. 4:03 And then we'll pass in for our second parameter our BirdSearch, 4:05 and we'll call that search. 4:11 Okay, let's see if we can do our entire search in one link expression. 4:16 That'll start out with a return, and then from the source. 4:24 We can start out by filtering with common name, 4:30 return source.Where I'll use s for 4:34 source, so s is an element inside the source enumerable. 4:40 S goes to s.CommonName == search, 4:46 which is our bird search, .CommonName. 4:51 What about if someone entered a partial name like the first three letters, 4:59 we should use the string method contains to return on a partial match. 5:03 So let's redo that. 5:08 Where s.CommonName.contains 5:12 search.CommonName. 5:18 That way, if I entered in S-P-A, it would return sparrows. 5:24 Well, what if somebody left the field for name blank? 5:29 When we search for my bird, we don't know what the name is, so 5:34 we'll need to check if the search common name property is null first. 5:37 So where S goes to search.CommonName 5:44 == null or it has a match. 5:50 That looks good. 5:55 Next let's write another where clause for the country. 5:57 I like to line up my link methods together like this. 6:01 Where s goes to and we'll check also if the country's null, 6:05 so search.Country == null or s. 6:13 Now, the country property is actually not on the bird itself, but 6:18 it's on the habitat, and let's go check out that class real quick. 6:22 Here we've got a list of places as habitats, so 6:29 it's got a list of habitats which are type place. 6:34 So let's check out the Place class and it's gotta string of countries, 6:40 so we're gonna have to use the any operator here. 6:45 So where the bird, which is the S its habitats, 6:48 are there any of those? 6:54 We use h here for habitat, h goes to h.Country. 6:56 We'll do a partial match on that too, contains search.Country. 7:02 Okay, that looks good. 7:11 Now, let's do our size parameter where S goes to. 7:14 We'll also check and make sure it's not null. 7:21 Or this time I think we'll do an exact match. 7:26 B.size == 7:31 search.Size. 7:35 Okay, next we need to narrow down by colors. 7:40 This is gonna be a little trickier because we've got multiple color fields on our 7:42 bird class and the bird search variable has a list of possible colours. 7:46 We'll start out with primary colour. 7:51 If any of our search colors is the primary color, 7:54 we'll want to include that bird in the result. 7:57 Ha, I just saw the operator we should use, any. 8:00 But since we want to return birds, if the colors match any of the primary, 8:02 secondary or tertiary colours, 8:07 we'll want to put all of those conditions within the same where clause. 8:09 So .Where(s goes to, we'll start 8:17 out with the search.Colors if any 8:22 of those where c, we'll use c for 8:27 color goes to c == s.PrimaryColor. 8:32 All right, but we won't close the where just then, 8:38 we're gonna put in or because if it's the primary color or 8:44 the secondary color, we wanna return both. 8:51 So S goes to search.Colors.Any where c goes to 8:56 same deal == SecondaryColor, okay. 9:01 Missed my s or so now we have to figure 9:05 out how to handle the tertiary colors. 9:10 Since we need to compare a list of colors with another list of colors, 9:16 it sounds like we need to use a join. 9:20 Let's try that out. 9:23 Ope, looks like I've specified that too many times, good thing I caught that. 9:25 Okay, so we don't need the s goes to. 9:30 We can start right there and say where the search.Colors, 9:33 then we'll join the list of colors from the search parameters 9:38 to s.TeriaryColors. 9:44 And we'll say sc for search color goes to sc, and then 9:48 tc for tertiary colors goes to tc, those are just a list of strings. 9:56 So we don't need to use any properties for the key selectors. 10:01 Now, for our result, 10:05 both parameters sc and tc goes to sc. 10:09 So when we join the search colors and 10:17 the tertiary colors together, if there's a match, it will return the matching color. 10:19 And all we care about is if there's at least one, so we can tack on the any 10:24 operator to return a boolean if that's the case, .Any. 10:29 Okay, so all of our colors are in our filter. 10:35 Finally, we need to deal with the page and page size perimeters. 10:40 Do you remember the operators skip and take? 10:45 Skip will skip a number of elements in the sequence and 10:48 take will specify how many elements to return. 10:51 So .Skip page 10:54 * pageSize. 11:00 So we're gonna start out on page zero, and when we use a page size of say five, 11:05 zero times five is zero, so it's not gonna skip any of the elements. 11:11 But once we advance to page one, page it would be one, pageSize will be five. 11:16 It'll skip ahead five elements and that'll bring us to the next page. 11:21 Then, our final take, and that'll just be the pageSize. 11:27 So if pageSize is five, then we'll take five elements. 11:32 And we did it, we put all of our search logic into one link expression. 11:37 Awesome job. 11:42
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