Csharp/CSharp Tutorial/LINQ/Query — различия между версиями
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Версия 18:31, 26 мая 2010
Содержание
- 1 All employees in a tree are grouped by department
- 2 ArrayList Query
- 3 Chaining Query Operators/extracts all strings containing the letter "a", sorts them by length, and then converts the results to uppercase
- 4 Complex Query Using Method Syntax
- 5 Conduct query on the result again
- 6 Get Distinct departments with condition
- 7 Join Query
- 8 query with extension methods
- 9 Use a LINQ query to find the public enums
- 10 Use Contains, Length and ToUpper from Linq
- 11 Use from where select to choose the Employees in the IT department from a tree
- 12 Use LINQ to get Employees in the IT department from a tree
- 13 Use select to retrieve all nodes in a Binary tree
All employees in a tree are grouped by department
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
public Tree(TreeNode nodeValue) { this.NodeData = nodeValue; this.LeftTree = null; this.RightTree = null; } public void Insert(TreeNode newItem) { TreeNode currentNodeValue = this.NodeData; if (currentNodeValue.rupareTo(newItem) > 0) { if (this.LeftTree == null) { this.LeftTree = new Tree<TreeNode>(newItem); } else { this.LeftTree.Insert(newItem); } } else { if (this.RightTree == null) { this.RightTree = new Tree<TreeNode>(newItem); } else { this.RightTree.Insert(newItem); } } } public void WalkTree() { if (this.LeftTree != null) { this.LeftTree.WalkTree(); } Console.WriteLine(this.NodeData.ToString()); if (this.RightTree != null) { this.RightTree.WalkTree(); } } public TreeNode NodeData { get; set; } public Tree<TreeNode> LeftTree { get; set; } public Tree<TreeNode> RightTree { get; set; }
IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() { if (this.LeftTree != null) { foreach (TreeNode item in this.LeftTree) { yield return item; } } yield return this.NodeData; if (this.RightTree != null) { foreach (TreeNode item in this.RightTree) { yield return item; } } } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw new NotImplementedException(); }
} class Employee : IComparable<Employee> {
public string FirstName { get; set; } public string LastName { get; set; } public string Department { get; set; } public int Id { get; set; } public override string ToString() { return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department); } int IComparable<Employee>.rupareTo(Employee other) { if (other == null) return 1; if (this.Id > other.Id) return 1; if (this.Id < other.Id) return -1; return 0; }
} class Program {
static void Main() { Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" }); empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" }); empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" }); empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" }); empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" }); empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" }); var employeesByDept = empTree.GroupBy(e => e.Department); foreach (var dept in employeesByDept) { Console.WriteLine("Department: {0}", dept.Key); foreach (var emp in dept) { Console.WriteLine("\t{0} {1}", emp.FirstName, emp.LastName); } } }
}</source>
ArrayList Query
<source lang="csharp">using System; using System.Collections; using System.ruponentModel;
public class Product { string name; public string Name { get { return name; } } decimal price; public decimal Price { get { return price; } } public Product(string name, decimal price) { this.name = name; this.price = price; } public static ArrayList GetSampleProducts() { ArrayList list = new ArrayList(); list.Add(new Product("C", 9.99m)); list.Add(new Product("A", 1.99m)); list.Add(new Product("F", 2.99m)); list.Add(new Product("S", 3.99m)); return list; } public override string ToString() { return string.Format("{0}: {1}", name, price); } } class ArrayListQuery { static void Main() { ArrayList products = Product.GetSampleProducts(); foreach (Product product in products) { if (product.Price > 10m) { Console.WriteLine(product); } } } }</source>
Chaining Query Operators/extracts all strings containing the letter "a", sorts them by length, and then converts the results to uppercase
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; class LinqDemo {
static void Main() { string[] names = { "J", "P", "G", "P" }; IEnumerable<string> query = names .Where(n => n.Contains("a")) .OrderBy(n => n.Length) .Select(n => n.ToUpper()); foreach (string name in query) Console.Write(name + "|"); }
}</source>
Complex Query Using Method Syntax
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text;
public class Customer { public string FirstName { get; set; } public string LastName { get; set; } public string EmailAddress { get; set; } public override string ToString(){ return string.Format("{0} {1}\nEmail: {2}",FirstName, LastName, EmailAddress); } } public class Address { public string Name { get; set; } public string Street { get; set; } public string City { get; set; } public override string ToString() { return string.Format("{0}, {1}", Street, City); } } public class Tester { static void Main() { List<Customer> customers = new List<Customer> { new Customer { FirstName = "A", LastName = "B", EmailAddress = "o@a.ru"}, new Customer { FirstName = "B", LastName = "C", EmailAddress = "k@a.ru" }, new Customer { FirstName = "D", LastName = "C", EmailAddress = "d@a.ru" }, new Customer { FirstName = "F", LastName = "G", EmailAddress = "j@a.ru" }, new Customer { FirstName = "L", LastName = "H", EmailAddress = "l@a.ru" } }; List<Address> addresses = new List<Address> { new Address { Name = "J", Street = "165 Main", City = "City 1" }, new Address { Name = "K H", Street = "3207 Way", City = "Cith 2" }, new Address { Name = "J G", Street = "800 Blvd.", City = "City 3" }, new Address { Name = "Mary", Street = "7 Ave", City = "City 4" }, new Address { Name = "Kate", Street = "2251 Avenue", City = "City 5" } }; var result = customers.Join(addresses, customer => string.Format("{0} {1}", customer.FirstName, customer.LastName), address => address.Name, (customer, address) => new { Customer = customer, Address = address }) .OrderBy(ca => ca.Customer.LastName) .ThenByDescending(ca => ca.Address.Street); foreach (var ca in result) { Console.WriteLine(string.Format("{0}\nAddress: {1}",ca.Customer, ca.Address)); } } }</source>
Conduct query on the result again
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text;
class Customer { public string ID { get; set; } public string City { get; set; } public string Country { get; set; } public string Region { get; set; } public decimal Sales { get; set; } } class Program { static void Main(string[] args) { List<Customer> customers = new List<Customer> { new Customer { ID="Q", City="London", Country="UK", Region="Europe", Sales=8000 }, new Customer { ID="R", City="Beijing", Country="China", Region="Asia", Sales=9000 }, new Customer { ID="T", City="Lima", Country="Peru", Region="South America", Sales=2002 } }; var queryResults = from c in customers group c by c.Region into cg select new { TotalSales = cg.Sum(c => c.Sales), Region = cg.Key } ; var orderedResults = from cg in queryResults orderby cg.TotalSales descending select cg ; foreach (var item in orderedResults) { Console.WriteLine(item.TotalSales + "\t: " + item.Region); } } }</source>
Get Distinct departments with condition
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
public Tree(TreeNode nodeValue) { this.NodeData = nodeValue; this.LeftTree = null; this.RightTree = null; } public void Insert(TreeNode newItem) { TreeNode currentNodeValue = this.NodeData; if (currentNodeValue.rupareTo(newItem) > 0) { if (this.LeftTree == null) { this.LeftTree = new Tree<TreeNode>(newItem); } else { this.LeftTree.Insert(newItem); } } else { if (this.RightTree == null) { this.RightTree = new Tree<TreeNode>(newItem); } else { this.RightTree.Insert(newItem); } } } public void WalkTree() { if (this.LeftTree != null) { this.LeftTree.WalkTree(); } Console.WriteLine(this.NodeData.ToString()); if (this.RightTree != null) { this.RightTree.WalkTree(); } } public TreeNode NodeData { get; set; } public Tree<TreeNode> LeftTree { get; set; } public Tree<TreeNode> RightTree { get; set; }
IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() { if (this.LeftTree != null) { foreach (TreeNode item in this.LeftTree) { yield return item; } } yield return this.NodeData; if (this.RightTree != null) { foreach (TreeNode item in this.RightTree) { yield return item; } } } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw new NotImplementedException(); }
} class Employee : IComparable<Employee> {
public string FirstName { get; set; } public string LastName { get; set; } public string Department { get; set; } public int Id { get; set; } public override string ToString() { return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department); } int IComparable<Employee>.rupareTo(Employee other) { if (other == null) return 1; if (this.Id > other.Id) return 1; if (this.Id < other.Id) return -1; return 0; }
} class Program {
static void Main() { Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" }); empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" }); empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" }); empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" }); empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" }); empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" }); var depts = empTree.Select(d => d.Department).Distinct(); foreach (var dept in depts) Console.WriteLine("Department: {0}", dept); }
}</source>
Join Query
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text;
class Customer { public string ID { get; set; } public string City { get; set; } public string Country { get; set; } public string Region { get; set; } public decimal Sales { get; set; } } class Order { public string ID { get; set; } public decimal Amount { get; set; } } class Program { static void Main(string[] args) { List<Order> orders = new List<Order> { new Order { ID="X", Amount=900 }, new Order { ID="Y", Amount=1000 }, new Order { ID="Z", Amount=1100 } }; List<Customer> customers = new List<Customer> { new Customer { ID="X", City="Beijing", Country="China", Region="Asia", Sales=9000 }, new Customer { ID="Y", City="Bogotá", Country="Colombia", Region="South America", Sales=1001 }, new Customer { ID="Z", City="Lima", Country="Peru", Region="South America", Sales=2002 } }; var queryResults = from c in customers join o in orders on c.ID equals o.ID select new { c.ID, c.City, SalesBefore = c.Sales, NewOrder = o.Amount, SalesAfter = c.Sales+o.Amount }; foreach (var item in queryResults) { Console.WriteLine(item); } } }</source>
query with extension methods
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text;
public class Customer { public string FirstName { get; set; } public string LastName { get; set; } public string EmailAddress { get; set; } public override string ToString() { return string.Format("{0} {1}\nEmail: {2}",FirstName, LastName, EmailAddress); } } public class Tester { static void Main() { List<Customer> customers = new List<Customer>{ new Customer { FirstName = "A", LastName = "B", EmailAddress = "o@a.ru"}, new Customer { FirstName = "B", LastName = "C", EmailAddress = "k@a.ru" }, new Customer { FirstName = "D", LastName = "C", EmailAddress = "d@a.ru" }, new Customer { FirstName = "F", LastName = "G", EmailAddress = "j@a.ru" }, new Customer { FirstName = "L", LastName = "H", EmailAddress = "l@a.ru" } }; IEnumerable<Customer> result = customers.Where(customer => customer.FirstName == "Donna"); foreach (Customer customer in result) Console.WriteLine(customer.ToString()); } }</source>
Use a LINQ query to find the public enums
<source lang="csharp">using System; using System.Reflection; using System.IO; using System.Linq;
public class MainClass { static void Main(string[] args) { string displayName = null; displayName = "System.Windows.Forms,Version=2.0.0.0,PublicKeyToken=b77a5c561934e089,Culture=\"\""; Assembly a = Assembly.Load(displayName); Type[] types = a.GetTypes(); var publicEnums = from pe in types where pe.IsEnum && pe.IsPublic select pe; foreach (var pe in publicEnums) { Console.WriteLine(pe); } } }</source>
Use Contains, Length and ToUpper from Linq
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; public class MainClass {
public static void Main() { string[] names = { "Tom", "Dick", "Harry", "Mary", "Jay" }; IEnumerable<string> filtered = names.Where(n => n.Contains("a")); IEnumerable<string> sorted = filtered.OrderBy(n => n.Length); IEnumerable<string> finalQuery = sorted.Select(n => n.ToUpper()); foreach (string name in filtered) Console.Write(name + "|"); Console.WriteLine(); foreach (string name in sorted) Console.Write(name + "|"); Console.WriteLine(); foreach (string name in finalQuery) Console.Write(name + "|"); }
}</source>
Use from where select to choose the Employees in the IT department from a tree
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
public Tree(TreeNode nodeValue) { this.NodeData = nodeValue; this.LeftTree = null; this.RightTree = null; } public void Insert(TreeNode newItem) { TreeNode currentNodeValue = this.NodeData; if (currentNodeValue.rupareTo(newItem) > 0) { if (this.LeftTree == null) { this.LeftTree = new Tree<TreeNode>(newItem); } else { this.LeftTree.Insert(newItem); } } else { if (this.RightTree == null) { this.RightTree = new Tree<TreeNode>(newItem); } else { this.RightTree.Insert(newItem); } } } public void WalkTree() { if (this.LeftTree != null) { this.LeftTree.WalkTree(); } Console.WriteLine(this.NodeData.ToString()); if (this.RightTree != null) { this.RightTree.WalkTree(); } } public TreeNode NodeData { get; set; } public Tree<TreeNode> LeftTree { get; set; } public Tree<TreeNode> RightTree { get; set; }
IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() { if (this.LeftTree != null) { foreach (TreeNode item in this.LeftTree) { yield return item; } } yield return this.NodeData; if (this.RightTree != null) { foreach (TreeNode item in this.RightTree) { yield return item; } } } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw new NotImplementedException(); }
} class Employee : IComparable<Employee> {
public string FirstName { get; set; } public string LastName { get; set; } public string Department { get; set; } public int Id { get; set; } public override string ToString() { return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department); } int IComparable<Employee>.rupareTo(Employee other) { if (other == null) return 1; if (this.Id > other.Id) return 1; if (this.Id < other.Id) return -1; return 0; }
} class Program {
static void Main() { Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" }); empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" }); empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" }); empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" }); empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" }); empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" }); var ITEmployees = from e in empTree where String.Equals(e.Department, "IT") select e; foreach (var emp in ITEmployees) Console.WriteLine(emp); }
}</source>
Use LINQ to get Employees in the IT department from a tree
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
public Tree(TreeNode nodeValue) { this.NodeData = nodeValue; this.LeftTree = null; this.RightTree = null; } public void Insert(TreeNode newItem) { TreeNode currentNodeValue = this.NodeData; if (currentNodeValue.rupareTo(newItem) > 0) { if (this.LeftTree == null) { this.LeftTree = new Tree<TreeNode>(newItem); } else { this.LeftTree.Insert(newItem); } } else { if (this.RightTree == null) { this.RightTree = new Tree<TreeNode>(newItem); } else { this.RightTree.Insert(newItem); } } } public void WalkTree() { if (this.LeftTree != null) { this.LeftTree.WalkTree(); } Console.WriteLine(this.NodeData.ToString()); if (this.RightTree != null) { this.RightTree.WalkTree(); } } public TreeNode NodeData { get; set; } public Tree<TreeNode> LeftTree { get; set; } public Tree<TreeNode> RightTree { get; set; }
IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() { if (this.LeftTree != null) { foreach (TreeNode item in this.LeftTree) { yield return item; } } yield return this.NodeData; if (this.RightTree != null) { foreach (TreeNode item in this.RightTree) { yield return item; } } } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw new NotImplementedException(); }
} class Employee : IComparable<Employee> {
public string FirstName { get; set; } public string LastName { get; set; } public string Department { get; set; } public int Id { get; set; } public override string ToString() { return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department); } int IComparable<Employee>.rupareTo(Employee other) { if (other == null) return 1; if (this.Id > other.Id) return 1; if (this.Id < other.Id) return -1; return 0; }
} class Program {
static void Main() { Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" }); empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" }); empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" }); empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" }); empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" }); empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" }); var ITEmployees = empTree.Where(e => String.Equals(e.Department, "IT")).Select(emp => emp); foreach (var emp in ITEmployees) Console.WriteLine(emp); }
}</source>
Use select to retrieve all nodes in a Binary tree
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
public Tree(TreeNode nodeValue) { this.NodeData = nodeValue; this.LeftTree = null; this.RightTree = null; } public void Insert(TreeNode newItem) { TreeNode currentNodeValue = this.NodeData; if (currentNodeValue.rupareTo(newItem) > 0) { if (this.LeftTree == null) { this.LeftTree = new Tree<TreeNode>(newItem); } else { this.LeftTree.Insert(newItem); } } else { if (this.RightTree == null) { this.RightTree = new Tree<TreeNode>(newItem); } else { this.RightTree.Insert(newItem); } } } public void WalkTree() { if (this.LeftTree != null) { this.LeftTree.WalkTree(); } Console.WriteLine(this.NodeData.ToString()); if (this.RightTree != null) { this.RightTree.WalkTree(); } } public TreeNode NodeData { get; set; } public Tree<TreeNode> LeftTree { get; set; } public Tree<TreeNode> RightTree { get; set; }
IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() { if (this.LeftTree != null) { foreach (TreeNode item in this.LeftTree) { yield return item; } } yield return this.NodeData; if (this.RightTree != null) { foreach (TreeNode item in this.RightTree) { yield return item; } } } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw new NotImplementedException(); }
} class Employee : IComparable<Employee> {
public string FirstName { get; set; } public string LastName { get; set; } public string Department { get; set; } public int Id { get; set; } public override string ToString() { return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department); } int IComparable<Employee>.rupareTo(Employee other) { if (other == null) return 1; if (this.Id > other.Id) return 1; if (this.Id < other.Id) return -1; return 0; }
} class Program {
static void Main() { Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" }); empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" }); empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" }); empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" }); empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" }); empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" }); var allEmployees = from e in empTree.ToList<Employee>() select e; foreach (var emp in allEmployees) Console.WriteLine(emp); }
}</source>