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POOpa: How to Interact With the Database Without Blocking the UI
 

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    <h2>The Setup</h2> <p>I have a (rather standard) form that allows a user to create an account by entering a username and password. When the <code>#username</code> field loses focus, the database is queried to see if the supplied username is available. </p> <h2>The Problem</h2> <p>Everything works as expected, but the user interface is blocked from when the <code>onblur</code> event of <code>#username</code> is triggered until the database returns a value. How can check the database in an asyncronous and non-blocking fashion?</p> <p>Here's my code (I've pulled most of this code out of example Opa projects):</p> <h3>Types</h3> <pre><code>@abstract type User.ref = string type User.t = { username : string ; passwd : string } type User.map('a) = ordered_map(User.ref, 'a, String.order) </code></pre> <h3>Database</h3> <pre><code>db /user : User.map(User.t) </code></pre> <h3>Form</h3> <pre><code>&lt;form&gt; &lt;input id=#username type="text" onblur={_ -&gt; username_available() } placeholder="username" /&gt; &lt;input id=#password type="password" placeholder="password" /&gt; &lt;/form&gt; </code></pre> <h3>Actions</h3> <pre><code>username_available() : void = user = Dom.get_value(#username) match (get_user(user)) with | { none } -&gt; Log.notice("username available:", "YES") | { some = _ } -&gt; Log.notice("username available:", "NO") get_user(username : string) : option(User.t) = match ?/user[username] with | { none } -&gt; Option.none | { ~some } -&gt; Option.some(some) </code></pre> <p>Thanks for your help.</p>
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