C#, LINQ, 2個Table Join 使用2個欄位條件Join

2個Table Join 使用2個欄位條件Join

• join的欄位名稱要相同

範例1:

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        // 假设有两个表格
        List<Table1> table1Data = new List<Table1>
        {
            new Table1 { ID = 1, Name = "John" },
            new Table1 { ID = 2, Name = "Alice" },
            new Table1 { ID = 3, Name = "Bob" }
        };

        List<Table2> table2Data = new List<Table2>
        {
            new Table2 { ID = 1, Age = 25 },
            new Table2 { ID = 2, Age = 30 },
            new Table2 { ID = 3, Age = 28 }
        };

        // 使用 LINQ 进行两个表格的连接
        var query = from t1 in table1Data
                    join t2 in table2Data on new { t1.ID, t1.Name } equals new { t2.ID, Name = "John" }
                    select new { t1.ID, t1.Name, t2.Age };

        // 打印结果
        foreach (var result in query)
        {
            Console.WriteLine($"ID: {result.ID}, Name: {result.Name}, Age: {result.Age}");
        }
    }
}

// 表格1
class Table1
{
    public int ID { get; set; }
    public string Name { get; set; }
}

// 表格2
class Table2
{
    public int ID { get; set; }
    public int Age { get; set; }
}

範例2:

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        // 建立一些示例資料
        List<Person> persons = new List<Person>
        {
            new Person { PersonId = 1, Name = "John", Age = 25 },
            new Person { PersonId = 2, Name = "Jane", Age = 30 },
            new Person { PersonId = 3, Name = "Bob", Age = 28 }
        };

        List<Contact> contacts = new List<Contact>
        {
            new Contact { PersonId = 1, Name = "John", Email = "john@example.com" },
            new Contact { PersonId = 2, Name = "Jane", Email = "jane@example.com" },
            new Contact { PersonId = 3, Name = "Bob", Email = "bob@example.com" }
        };

        // 使用 LINQ 進行兩個表格的聯結
        var query = from person in persons
                    join contact in contacts
                    on new { person.PersonId, person.Name } equals new { contact.PersonId, Name = contact.Name }
                    select new
                    {
                        person.PersonId,
                        person.Name,
                        person.Age,
                        contact.Email
                    };

        // 輸出結果
        foreach (var result in query)
        {
            Console.WriteLine($"{result.PersonId} - {result.Name}, Age: {result.Age}, Email: {result.Email}");
        }
    }
}

// 定義 Person 類別
class Person
{
    public int PersonId { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

// 定義 Contact 類別
class Contact
{
    public int PersonId { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
}