C# Tutorial 15
In this video I’ll cover LINQ. Language Integrated Query (LINQ) provides many tools for working with data. LINQ is similar to SQL, but it can work with data aside from databases. I’ll cover From, Where, Orderby, Select, In, Inner Joins, Group Inner Join, Equals and using LINQ with multiple different collections.
For best results take notes on the cheat sheet provided above as you watch and leave any questions you have.
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Code & Transcript
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// ---------- Animal.cs ---------- namespace CSharpTutA.cs { class Animal { public string Name { get; set; } public double Weight { get; set; } public double Height { get; set; } public int AnimalID { get; set; } public Animal(string name = "No Name", double weight = 0, double height = 0) { Name = name; Weight = weight; Height = height; } public override string ToString() { return string.Format("{0} weighs {1}lbs and is {2} inches tall", Name, Weight, Height); } } } // ---------- Owner.cs ---------- namespace CSharpTutA.cs { class Owner { public string Name { get; set; } public int OwnerID { get; set; } } } // ---------- Program.cs ---------- using System; using System.Linq; using System.Collections; using System.Collections.Generic; namespace CSharpTutA.cs { // Language Integrated Query (LINQ) provides // many tools for working with data // LINQ is similar to SQL, but it can work // with data aside from databases // You manipulate data using Query Expressions class Program { static void Main(string[] args) { QueryStringArray(); // Get the array returned and print it int[] intArray = QueryIntArray(); foreach(int i in intArray) Console.WriteLine(i); Console.WriteLine(); QueryArrayList(); QueryCollection(); QueryAnimalData(); Console.ReadLine(); } static void QueryStringArray() { string[] dogs = {"K 9", "Brian Griffin", "Scooby Doo", "Old Yeller", "Rin Tin Tin", "Benji", "Charlie B. Barkin", "Lassie", "Snoopy"}; // Get strings with spaces and put in // alphabetical order // from states where data comes from and // where to store each piece as you cycle // where defines conditions that must be met // orderby defines what data is used for // ordering results (ascending / descending) // select defines the variable that is // checked against the condition var dogSpaces = from dog in dogs where dog.Contains(" ") orderby dog descending select dog; foreach(var i in dogSpaces) { Console.WriteLine(i); } Console.WriteLine(); } static int[] QueryIntArray() { int[] nums = { 5, 10, 15, 20, 25, 30, 35 }; // Get numbers bigger then 20 var gt20 = from num in nums where num > 20 orderby num select num; foreach(var i in gt20) { Console.WriteLine(i); } Console.WriteLine(); // The type is an enumerable Console.WriteLine($"Get Type : {gt20.GetType()}"); // You can convert it into a List or array var listGT20 = gt20.ToList<int>(); var arrayGT20 = gt20.ToArray(); // If you change the data the query // automatically updates nums[0] = 40; foreach (var i in gt20) { Console.WriteLine(i); } Console.WriteLine(); return arrayGT20; } static void QueryArrayList() { ArrayList famAnimals = new ArrayList() { new Animal{Name = "Heidi", Height = .8, Weight = 18}, new Animal { Name = "Shrek", Height = 4, Weight = 130 }, new Animal { Name = "Congo", Height = 3.8, Weight = 90 } }; // You have to convert the ArrayList into // an IEnumerable var famAnimalEnum = famAnimals.OfType<Animal>(); var smAnimals = from animal in famAnimalEnum where animal.Weight <= 90 orderby animal.Name select animal; foreach(var animal in smAnimals) { Console.WriteLine("{0} weighs {1}lbs", animal.Name, animal.Weight); } Console.WriteLine(); } static void QueryCollection() { var animalList = new List<Animal>() { new Animal{Name = "German Shepherd", Height = 25, Weight = 77}, new Animal{Name = "Chihuahua", Height = 7, Weight = 4.4}, new Animal{Name = "Saint Bernard", Height = 30, Weight = 200} }; var bigDogs = from dog in animalList where (dog.Weight > 70) && (dog.Height > 25) orderby dog.Name select dog; foreach(var dog in bigDogs) { Console.WriteLine("A {0} weighs {1}lbs", dog.Name, dog.Weight); } Console.WriteLine(); } static void QueryAnimalData() { Animal[] animals = new[] { new Animal{Name = "German Shepherd", Height = 25, Weight = 77, AnimalID = 1}, new Animal{Name = "Chihuahua", Height = 7, Weight = 4.4, AnimalID = 2}, new Animal{Name = "Saint Bernard", Height = 30, Weight = 200, AnimalID = 3}, new Animal{Name = "Pug", Height = 12, Weight = 16, AnimalID = 1}, new Animal{Name = "Beagle", Height = 15, Weight = 23, AnimalID = 2} }; Owner[] owners = new[] { new Owner{Name = "Doug Parks", OwnerID = 1}, new Owner{Name = "Sally Smith", OwnerID = 2}, new Owner{Name = "Paul Brooks", OwnerID = 3} }; // Remove name and height var nameHeight = from a in animals select new { a.Name, a.Height }; // Convert to an object array Array arrNameHeight = nameHeight.ToArray(); foreach (var i in arrNameHeight) { Console.WriteLine(i.ToString()); } Console.WriteLine(); // Create an inner join // Join info in owners and animals using // equal values for IDs // Store values for animal and owner var innerJoin = from animal in animals join owner in owners on animal.AnimalID equals owner.OwnerID select new { OwnerName = owner.Name, AnimalName = animal.Name }; foreach (var i in innerJoin) { Console.WriteLine("{0} owns {1}", i.OwnerName, i.AnimalName); } Console.WriteLine(); // Create a group inner join // Get all animals and put them in a // newly created owner group if their // IDs match the owners ID var groupJoin = from owner in owners orderby owner.OwnerID join animal in animals on owner.OwnerID equals animal.AnimalID into ownerGroup select new { Owner = owner.Name, Animals = from owner2 in ownerGroup orderby owner2.Name select owner2 }; int totalAnimals = 0; foreach (var ownerGroup in groupJoin) { Console.WriteLine(ownerGroup.Owner); foreach (var animal in ownerGroup.Animals) { totalAnimals++; Console.WriteLine("* {0}", animal.Name); } } } } } |
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