{"id":1117,"date":"2023-03-19T21:15:27","date_gmt":"2023-03-19T14:15:27","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=1117"},"modified":"2023-06-26T15:50:07","modified_gmt":"2023-06-26T08:50:07","slug":"linq-inner-join","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-linq\/linq-inner-join\/","title":{"rendered":"LINQ Inner Join"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you&#8217;ll learn how to use the LINQ <code>Join()<\/code> method to perform an inner join of two sequences based on one or more keys.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Introduction to the LINQ Inner Join <\/h2>\n\n\n\n<p>To join two sequences based on one or more keys, you use the LINQ <code>Join()<\/code> extension method. Here&#8217;s the syntax of the <code>Join()<\/code> method:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">static<\/span> IEnumerable&lt;TResult&gt; Join&lt;TOuter,TInner,TKey,TResult&gt; (\n    <span class=\"hljs-keyword\">this<\/span> IEnumerable&lt;TOuter&gt; outer, \n    IEnumerable&lt;TInner&gt; inner, \n    Func&lt;TOuter,TKey&gt; outerKeySelector, \n    Func&lt;TInner,TKey&gt; innerKeySelector, \n    Func&lt;TOuter,TInner,TResult&gt; resultSelector\n);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>In this syntax:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>outer<\/code> is the first sequence to join.<\/li>\n\n\n\n<li><code>inner<\/code> is the sequence that joins to the first sequence.<\/li>\n\n\n\n<li><code>outerKeySelector<\/code> is a function that extracts the join key from each element of the first sequence.<\/li>\n\n\n\n<li><code>innerKeySelector<\/code> is a function that extracts the join key from each element of the second sequence.<\/li>\n\n\n\n<li><code>resultSelector<\/code> is a function that creates the result element from two matching elements.<\/li>\n<\/ul>\n\n\n\n<p>The <code>Join()<\/code> method returns an <code><a href=\"https:\/\/csharptutorial.net\/csharp-linq\/csharp-ienumerable\/\">IEnumerable&lt;TResult&gt;<\/a><\/code> that has elements as the result of an inner join on the two sequences.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">LINQ Inner Join examples<\/h2>\n\n\n\n<p>Let&#8217;s take some examples of using the LINQ <code>Join()<\/code> method to perform an inner join.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">1) Using LINQ Join() method to perform an inner join based on a single key<\/h3>\n\n\n\n<p>The following program demonstrates how to use the <code>Join()<\/code> method to join the products list to the item list based on the product id:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Product<\/span>\n{\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">int<\/span> Id { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">string<\/span> Name { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">decimal<\/span> Cost { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-title\">Product<\/span>(<span class=\"hljs-params\"><span class=\"hljs-keyword\">int<\/span> id, <span class=\"hljs-keyword\">string<\/span> name, <span class=\"hljs-keyword\">decimal<\/span> cost<\/span>)<\/span>\n    {\n        Id = id;\n        Name = name;\n        Cost = cost;\n    }\n}\n\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Item<\/span>\n{\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">int<\/span> ProductId { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">int<\/span> Qty { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">decimal<\/span> Price { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-title\">Item<\/span>(<span class=\"hljs-params\"><span class=\"hljs-keyword\">int<\/span> productId, <span class=\"hljs-keyword\">int<\/span> qty, <span class=\"hljs-keyword\">decimal<\/span> price<\/span>)<\/span>\n    {\n        ProductId = productId;\n        Qty = qty;\n        Price = price;\n    }\n}\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Program<\/span>\n{\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">static<\/span> <span class=\"hljs-keyword\">void<\/span> <span class=\"hljs-title\">Main<\/span>(<span class=\"hljs-params\"><span class=\"hljs-keyword\">string<\/span>&#91;] args<\/span>)<\/span>\n    {\n        <span class=\"hljs-keyword\">var<\/span> products = <span class=\"hljs-keyword\">new<\/span> List&lt;Product&gt;()\n        {\n            <span class=\"hljs-keyword\">new<\/span> (id: <span class=\"hljs-number\">1<\/span>, name: <span class=\"hljs-string\">\"A\"<\/span>, cost: <span class=\"hljs-number\">10<\/span>),\n            <span class=\"hljs-keyword\">new<\/span> (id: <span class=\"hljs-number\">2<\/span>, name: <span class=\"hljs-string\">\"B\"<\/span>, cost: <span class=\"hljs-number\">20<\/span>),\n            <span class=\"hljs-keyword\">new<\/span> (id: <span class=\"hljs-number\">3<\/span>, name: <span class=\"hljs-string\">\"C\"<\/span>, cost: <span class=\"hljs-number\">30<\/span>)\n        };\n\n        <span class=\"hljs-keyword\">var<\/span> items = <span class=\"hljs-keyword\">new<\/span> List&lt;Item&gt;()\n        {\n            <span class=\"hljs-keyword\">new<\/span> (productId:<span class=\"hljs-number\">1<\/span>, qty: <span class=\"hljs-number\">2<\/span>, price: <span class=\"hljs-number\">12<\/span>),\n            <span class=\"hljs-keyword\">new<\/span> (productId:<span class=\"hljs-number\">2<\/span>, qty: <span class=\"hljs-number\">2<\/span>, price: <span class=\"hljs-number\">25<\/span>),\n            <span class=\"hljs-keyword\">new<\/span> (productId:<span class=\"hljs-number\">3<\/span>, qty: <span class=\"hljs-number\">4<\/span>, price: <span class=\"hljs-number\">35<\/span>)\n        };\n\n        <span class=\"hljs-keyword\">var<\/span> results = items.Join(\n           products,\n           item =&gt; item.ProductId,\n           product =&gt; product.Id,\n           (item, product) =&gt; <span class=\"hljs-keyword\">new<\/span>\n           {\n               product.Name,\n               product.Cost,\n               item.Price,\n               item.Qty,\n               Margin = (item.Price - product.Cost) * item.Qty\n           }\n       );\n\n        <span class=\"hljs-keyword\">foreach<\/span> (<span class=\"hljs-keyword\">var<\/span> result <span class=\"hljs-keyword\">in<\/span> results)\n        {\n            Console.WriteLine(result);\n        }\n\n    }\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>How it works.<\/p>\n\n\n\n<p>First, define a <code>Product<\/code> class that has three properties <code>Id<\/code>, <code>Name<\/code>, and <code>Cost<\/code>.<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Product<\/span>\n{\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">int<\/span> Id { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">string<\/span> Name { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">decimal<\/span> Cost { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-title\">Product<\/span>(<span class=\"hljs-params\"><span class=\"hljs-keyword\">int<\/span> id, <span class=\"hljs-keyword\">string<\/span> name, <span class=\"hljs-keyword\">decimal<\/span> cost<\/span>)<\/span>\n    {\n        Id = id;\n        Name = name;\n        Cost = cost;\n    }\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Second, define the <code>Item<\/code> class that has three properties <code>ProductId<\/code>, <code>Qty<\/code>, and <code>Price<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Item<\/span>\n{\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">int<\/span> ProductId { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">int<\/span> Qty { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">decimal<\/span> Price { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-title\">Item<\/span>(<span class=\"hljs-params\"><span class=\"hljs-keyword\">int<\/span> productId, <span class=\"hljs-keyword\">int<\/span> qty, <span class=\"hljs-keyword\">decimal<\/span> price<\/span>)<\/span>\n    {\n        ProductId = productId;\n        Qty = qty;\n        Price = price;\n    }\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>ProductId<\/code> of the <code>Item<\/code> class matches the <code>Id<\/code> of the <code>Product<\/code> class.<\/p>\n\n\n\n<p>Third, create a list of three <code>Product<\/code> objects in the <code>Main()<\/code> method of the <code>Program<\/code> class:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">var<\/span> products = <span class=\"hljs-keyword\">new<\/span> List&lt;Product&gt;()\n{\n    <span class=\"hljs-keyword\">new<\/span> (id: <span class=\"hljs-number\">1<\/span>, name: <span class=\"hljs-string\">\"A\"<\/span>, cost: <span class=\"hljs-number\">10<\/span>),\n    <span class=\"hljs-keyword\">new<\/span> (id: <span class=\"hljs-number\">2<\/span>, name: <span class=\"hljs-string\">\"B\"<\/span>, cost: <span class=\"hljs-number\">20<\/span>),\n    <span class=\"hljs-keyword\">new<\/span> (id: <span class=\"hljs-number\">3<\/span>, name: <span class=\"hljs-string\">\"C\"<\/span>, cost: <span class=\"hljs-number\">30<\/span>)\n};<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Fourth, create a list of three Items:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">var<\/span> items = <span class=\"hljs-keyword\">new<\/span> List&lt;Item&gt;()\n{\n    <span class=\"hljs-keyword\">new<\/span> (productId:<span class=\"hljs-number\">1<\/span>, qty: <span class=\"hljs-number\">2<\/span>, price: <span class=\"hljs-number\">12<\/span>),\n    <span class=\"hljs-keyword\">new<\/span> (productId:<span class=\"hljs-number\">2<\/span>, qty: <span class=\"hljs-number\">2<\/span>, price: <span class=\"hljs-number\">25<\/span>),\n    <span class=\"hljs-keyword\">new<\/span> (productId:<span class=\"hljs-number\">3<\/span>, qty: <span class=\"hljs-number\">4<\/span>, price: <span class=\"hljs-number\">35<\/span>)\n};<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Fifth, join the product list with the items list based on the product id:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">var<\/span> results = items.Join(\n    products,\n    item =&gt; item.ProductId,\n    product =&gt; product.Id,\n    (item, product) =&gt; <span class=\"hljs-keyword\">new<\/span>\n    {\n        product.Name,\n        product.Cost,\n        item.Price,\n        item.Qty,\n        Margin = (item.Price - product.Cost) * item.Qty\n    }\n);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>Join()<\/code> method joins the products and items list based on the common property:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>ProductId<\/code> in <code>Item<\/code> in the <code>items<\/code> list.<\/li>\n\n\n\n<li><code>Id<\/code> of <code>Product<\/code> in the <code>products<\/code> list.<\/li>\n<\/ul>\n\n\n\n<p>The result of the inner join is a new sequence of anonymous objects. Each object contains the data from matching <code>Item<\/code> and <code>Product<\/code> objects in both sequences.<\/p>\n\n\n\n<p>The <code>Join()<\/code> method takes four arguments:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>The first argument is the products list which is the sequence to join with.<\/li>\n\n\n\n<li>The second argument is a lambda expression that defines the matching property in the items list &#8211; <code>item=&gt; item.ProductId<\/code>.<\/li>\n\n\n\n<li>The third argument is a lambda expression that defines the matching property in the products list &#8211; <code>product =&gt; product.Id<\/code>.<\/li>\n\n\n\n<li>The fourth argument is a lambda expression that defines the shape of the result objects. Each anonymous object has four properties: <code>Name<\/code>, <code>Cost<\/code>, <code>Price<\/code>, <code>Qty<\/code>, and <code>Margin<\/code>. The <code>Margin<\/code> property represents the profit margin of each item based on the cost of the product and the price of the item.<\/li>\n<\/ol>\n\n\n\n<p>Finally, display the result of the join to the console using a <code><a href=\"https:\/\/csharptutorial.net\/csharp-tutorial\/csharp-foreach\/\">foreach<\/a><\/code> loop and <code>WriteLine()<\/code> method.<\/p>\n\n\n\n<p>The following shows the query syntax that is equivalent to the above method syntax:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">var<\/span> results = <span class=\"hljs-keyword\">from<\/span> product <span class=\"hljs-keyword\">in<\/span> products\n              <span class=\"hljs-keyword\">join<\/span> item <span class=\"hljs-keyword\">in<\/span> items <span class=\"hljs-keyword\">on<\/span> product.Id <span class=\"hljs-keyword\">equals<\/span> item.ProductId\n              <span class=\"hljs-keyword\">select<\/span> <span class=\"hljs-keyword\">new<\/span>\n              {\n                  product.Name,\n                  product.Cost,\n                  item.Price,\n                  item.Qty,\n                  Margin = (item.Price - product.Cost) * item.Qty\n              };<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h3 class=\"wp-block-heading\">2) Using LINQ Join() method to perform an inner join based on a composite key<\/h3>\n\n\n\n<p>The following program demonstrates how to use the <code>Join()<\/code> method to join the <code>candidates<\/code> and <code>employees<\/code> lists based on first name and last name:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Candidate<\/span>\n{\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">string<\/span> FirstName { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">string<\/span> LastName { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n\n    <span class=\"hljs-keyword\">public<\/span> DateTime InterviewDate { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-title\">Candidate<\/span>(<span class=\"hljs-params\"><span class=\"hljs-keyword\">string<\/span> firstName, <span class=\"hljs-keyword\">string<\/span> lastName, DateTime interviewDate<\/span>)<\/span>\n    {\n        FirstName = firstName;\n        LastName = lastName;\n        InterviewDate = interviewDate;\n    }\n}\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Employee<\/span>\n{\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">string<\/span> FirstName { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">string<\/span> LastName { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n\n    <span class=\"hljs-keyword\">public<\/span> DateTime JoinedDate { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>; }\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-title\">Employee<\/span>(<span class=\"hljs-params\"><span class=\"hljs-keyword\">string<\/span> firstName, <span class=\"hljs-keyword\">string<\/span> lastName, DateTime joinedDate<\/span>)<\/span>\n    {\n        FirstName = firstName;\n        LastName = lastName;\n        JoinedDate = joinedDate;\n    }\n}\n\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Program<\/span>\n{\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">static<\/span> <span class=\"hljs-keyword\">void<\/span> <span class=\"hljs-title\">Main<\/span>(<span class=\"hljs-params\"><span class=\"hljs-keyword\">string<\/span>&#91;] args<\/span>)<\/span>\n    {\n        <span class=\"hljs-comment\">\/\/ Create a list of candidates<\/span>\n        List&lt;Candidate&gt; candidates = <span class=\"hljs-keyword\">new<\/span>()\n        {\n            <span class=\"hljs-keyword\">new<\/span> (<span class=\"hljs-string\">\"John\"<\/span>, <span class=\"hljs-string\">\"Doe\"<\/span>, <span class=\"hljs-keyword\">new<\/span> DateTime(<span class=\"hljs-number\">2010<\/span>, <span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">20<\/span>)),\n            <span class=\"hljs-keyword\">new<\/span> (<span class=\"hljs-string\">\"Jane\"<\/span>, <span class=\"hljs-string\">\"Doe\"<\/span>, <span class=\"hljs-keyword\">new<\/span> DateTime(<span class=\"hljs-number\">2010<\/span>, <span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">28<\/span>)),\n            <span class=\"hljs-keyword\">new<\/span> (<span class=\"hljs-string\">\"Bob\"<\/span>, <span class=\"hljs-string\">\"Smith\"<\/span>,<span class=\"hljs-keyword\">new<\/span> DateTime(<span class=\"hljs-number\">2010<\/span>, <span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">15<\/span>))\n        };\n\n        <span class=\"hljs-comment\">\/\/ Create a list of employees<\/span>\n        List&lt;Employee&gt; employees = <span class=\"hljs-keyword\">new<\/span>()\n        {\n            <span class=\"hljs-keyword\">new<\/span> (<span class=\"hljs-string\">\"John\"<\/span>, <span class=\"hljs-string\">\"Doe\"<\/span>, <span class=\"hljs-keyword\">new<\/span> DateTime(<span class=\"hljs-number\">2010<\/span>, <span class=\"hljs-number\">2<\/span>, <span class=\"hljs-number\">1<\/span>)),\n            <span class=\"hljs-keyword\">new<\/span> (<span class=\"hljs-string\">\"Jane\"<\/span>, <span class=\"hljs-string\">\"Doe\"<\/span>, <span class=\"hljs-keyword\">new<\/span> DateTime(<span class=\"hljs-number\">2010<\/span>, <span class=\"hljs-number\">2<\/span>, <span class=\"hljs-number\">2<\/span>)),\n            <span class=\"hljs-keyword\">new<\/span> (<span class=\"hljs-string\">\"Alice\"<\/span>, <span class=\"hljs-string\">\"Johnson\"<\/span>, <span class=\"hljs-keyword\">new<\/span> DateTime(<span class=\"hljs-number\">2010<\/span>, <span class=\"hljs-number\">2<\/span>, <span class=\"hljs-number\">3<\/span>))\n        };\n\n        <span class=\"hljs-keyword\">var<\/span> query = candidates.Join(\n            employees,\n            candidate =&gt; <span class=\"hljs-keyword\">new<\/span> { candidate.FirstName, candidate.LastName },\n            employee =&gt; <span class=\"hljs-keyword\">new<\/span> { employee.FirstName, employee.LastName },\n            (candidate, employee) =&gt; <span class=\"hljs-keyword\">new<\/span>\n            {\n                Name = <span class=\"hljs-string\">$\"<span class=\"hljs-subst\">{candidate.FirstName}<\/span> <span class=\"hljs-subst\">{candidate.LastName}<\/span>\"<\/span>,\n                candidate.InterviewDate,\n                employee.JoinedDate\n            });\n\n\n        <span class=\"hljs-keyword\">foreach<\/span> (<span class=\"hljs-keyword\">var<\/span> result <span class=\"hljs-keyword\">in<\/span> query)\n        {\n            Console.WriteLine(<span class=\"hljs-string\">$\"<span class=\"hljs-subst\">{result.Name}<\/span> was interviewd on <span class=\"hljs-subst\">{result.InterviewDate.ToShortDateString()}<\/span> and joined on <span class=\"hljs-subst\">{result.JoinedDate.ToShortDateString()}<\/span>\"<\/span>);\n        }\n    }\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\">John Doe was interviewd <span class=\"hljs-keyword\">on<\/span> <span class=\"hljs-number\">1<\/span>\/<span class=\"hljs-number\">20<\/span>\/<span class=\"hljs-number\">2010<\/span> and joined <span class=\"hljs-keyword\">on<\/span> <span class=\"hljs-number\">2<\/span>\/<span class=\"hljs-number\">1<\/span>\/<span class=\"hljs-number\">2010<\/span>\nJane Doe was interviewd <span class=\"hljs-keyword\">on<\/span> <span class=\"hljs-number\">1<\/span>\/<span class=\"hljs-number\">28<\/span>\/<span class=\"hljs-number\">2010<\/span> and joined <span class=\"hljs-keyword\">on<\/span> <span class=\"hljs-number\">2<\/span>\/<span class=\"hljs-number\">2<\/span>\/<span class=\"hljs-number\">2010<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>In this example: <\/p>\n\n\n\n<p>First, define two classes: <code>Candidate<\/code> and <code>Employee<\/code>.<\/p>\n\n\n\n<p>Second, create two lists of candidates and employees that contain the <code>Candidate<\/code> and <code>Employee<\/code> objects respectively.<\/p>\n\n\n\n<p>Third, join the two lists based on the matching of the <code>FirstName<\/code> and <code>LastName<\/code> properties. The <code>Join()<\/code> method is called on the <code>candidates<\/code> list and takes four arguments:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The <code>employees<\/code> to join with.<\/li>\n\n\n\n<li>A lambda expression that selects the key of the <code>Candidate<\/code> object to join (<code>FirstName<\/code> and <code>LastName<\/code>)<\/li>\n\n\n\n<li>A lambda expression that selects the key of the <code>Employee<\/code> object to join (<code>FirstName<\/code> and <code>LastName<\/code>).<\/li>\n\n\n\n<li>A lambda expression that creates a new anonymous object for the result list. The anonymous object contains the <code>Name<\/code>, <code>InterviewDate<\/code>, and <code>JoinedDate<\/code> properties.<\/li>\n<\/ul>\n\n\n\n<p>Finally, iterate over the result and write each object to the console.<\/p>\n\n\n\n<p>The following shows the query syntax that is equivalent to the above method syntax:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">var<\/span> query = <span class=\"hljs-keyword\">from<\/span> candidate <span class=\"hljs-keyword\">in<\/span> candidates\n            <span class=\"hljs-keyword\">join<\/span> employee <span class=\"hljs-keyword\">in<\/span> employees\n            <span class=\"hljs-keyword\">on<\/span> <span class=\"hljs-keyword\">new<\/span> { candidate.FirstName, candidate.LastName }\n            <span class=\"hljs-keyword\">equals<\/span> <span class=\"hljs-keyword\">new<\/span> { employee.FirstName, employee.LastName }\n            <span class=\"hljs-keyword\">select<\/span> <span class=\"hljs-keyword\">new<\/span>\n            {\n                Name = <span class=\"hljs-string\">$\"<span class=\"hljs-subst\">{candidate.FirstName}<\/span> <span class=\"hljs-subst\">{candidate.LastName}<\/span>\"<\/span>,\n                candidate.InterviewDate,\n                employee.JoinedDate\n            };<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use LINQ <code>Join()<\/code> method to join two sequences based on one or more keys.<\/li>\n<\/ul>\n<div class=\"helpful-block-content\" 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