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" 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alt="Github"/></a></div></div></div></nav><div><section class="section"><div class="full-width-image-container margin-top-0" style="background-image:url(/static/blogging-ea4fdaec566aafddd0291352e3f8802d.jpg)"/><div class="tile is-ancestor"><div class="tile is-vertical is-7"><div class="tile"><div class="tile is-parent"><article class="tile is-child box"><div class="container content"><div class="columns"><div class="column is-10 is-offset-1"><h1 class="title is-size-2 has-text-weight-bold is-bold-light">Why Use DateTimeOffset</h1> Date Published: 17 January 2022<img src="/static/c8166182a364652dc4e8116239397bcd/4e530/why-use-datetimeoffset.png" alt="Why Use DateTimeOffset" width="100%"/><div>Raise your hand if you've stored entity values in a database as DateTime. Ok, everybody has their hand up. You can put your hand down - you look silly doing that while reading an article on some website. Using DateTime for entity properties and database fields is ubiquitous, but if you really care about the time portion of the value, it's often ambiguous. What time zone is the date in? Is it stored as UTC? From everywhere that touches it? How can you be sure? DateTimeOffset provides a solution to this problem. <h2>Storing DateTime Values</h2> The simple DateTime type (<a href="https://ardalis.com/datetime-as-a-value-object/">which makes a great example of a Value Object</a>), always assumes the local machine's relative time. When you ask it for <code class="language-text">.Today</code> or <code class="language-text">.Now</code> it uses the local system clock. This can easily cause problems between machines with different times and/or timezones. It can be helpful to look at the output of a particular DateTime value as a string. <div class="gatsby-highlight" data-language="csharp"><pre class="language-csharp"><code class="language-csharp">var rightNow = new DateTime(2022,1,17,18,11,30); Console.WriteLine(rightNow); // 1/17/2022 6:11:30 PM Console.WriteLine(rightNow.ToLocalTime()); // 1/17/2022 1:11:30 PM Console.WriteLine(rightNow.ToUniversalTime()); // 1/17/2022 11:11:30 PM Console.WriteLine(rightNow.ToString("yyyy-MM-ddTHH:mm:ss")); // 2022-01-17T18:11:30</code></pre></div> The initial time is 6:11pm on 17 Jan 2022 on my computer here in Ohio, which is Eastern Standard Time (UTC-5). The <code class="language-text">rightNow</code> variable doesn't include any time zone data in it. The <code class="language-text">DateTime</code> functions <code class="language-text">ToLocalTime</code> and <code class="language-text">ToUniversalTime</code> assume that the data they're operating is in UTC or local time, respectively. As a result, of the four different times shown, the one produced by <code class="language-text">ToLocalTime</code> is incorrect, since it's subtracting 5 hours from the actual time of 6:11pm. Note that when you store datetimes in your application, they'll be stored based on whatever machine timezone they're running on, unless you're extremely disciplined about using UTC times wherever you modify the dates. And even if you are, there's no way to look at your data and see that you were, after the fact. The data simply won't know. What happens when the same code is run on different developers' machines in different timezones? What happens when tests are run in this case? What happens when you move your cloud-hosted app from one region to another? What happens if the app spans region in production for high-availability (HA) reasons? For all of these reasons, it can be worthwhile to store dates in your application using the DateTimeOffset type. <h2>DateTimeOffset</h2> DateTimeOffset is both a .NET type and a SQL Server type (other databases have equivalents, too). The main difference between it and the simpler DateTime type we all know and love is that it includes a time zone offset from UTC. Thus, it's always clear when looking at a DateTimeOffset what time is meant, whether UTC or local. It is always clear what actual time is depicted by DateTimeOffset, whether it's UTC or local. Adding to the example above, it can be helpful to see what DateTimeOffset values look like when represented as strings: <div class="gatsby-highlight" data-language="csharp"><pre class="language-csharp"><code class="language-csharp">DateTimeOffset rightNowHere = new DateTimeOffset(rightNow); Console.WriteLine(rightNowHere); // 1/17/2022 6:11:30 PM -05:00 Console.WriteLine(rightNowHere.ToLocalTime()); // 1/17/2022 6:11:30 PM -05:00 Console.WriteLine(rightNowHere.ToUniversalTime()); // 1/17/2022 11:11:30 PM +00:00 Console.WriteLine(rightNowHere.ToString("yyyy-MM-ddTHH:mm:ss")); // 2022-01-17T18:11:30</code></pre></div> Two things to note in the listing above: the ToLocalTime value is correct and the standard ToString values all include the timezone offset (-05:00 when local, +00:00 when UTC). The last value's format string doesn't include the offset, which is represented in the format string as taking a nap: <code class="language-text">zzz</code>. <div class="gatsby-highlight" data-language="csharp"><pre class="language-csharp"><code class="language-csharp">Console.WriteLine(rightNowHere.ToString("yyyy'-'MM'-'dd'T'HH':'mm':'ss zzz")); // 2022-01-17T18:11:30 -05:00</code></pre></div> <h2>DateTimeOffset in SQL Server</h2> SQL Server supports both DateTime and DateTimeOffset values. DateTimeOffset uses variable precision and so can take up more space than DateTime, but doesn't always do so. <a href="https://database.guide/datetime-vs-datetimeoffset-in-sql-server-whats-the-difference/">Compare DateTimeOffset and DateTime on SQL Server</a> and choose which one makes sense for your needs. If you just want to quickly see the difference, run these queries: <div class="gatsby-highlight" data-language="sql"><pre class="language-sql"><code class="language-sql">select GetDate() select SYSDATETIME() select SYSDATETIMEOFFSET()</code></pre></div> Results (note precision difference in second and third result): <div class="gatsby-highlight" data-language="sql"><pre class="language-sql"><code class="language-sql">2022-01-17 18:30:18.227 2022-01-17 18:30:18.2292271 2022-01-17 18:30:18.2292271 -05:00</code></pre></div>