Typescript: index signature is missing in type when extending interface
<p>I'm trying to do an extension of one of my interfaces, but keep getting the error "index signature is missing in type {dcs: Relationship} with the following snippet:</p>

<pre><code>interface Relationship {
    data: {
        id: string;
        type: string;
    }
}

interface T {
    relationships: {[key: string]: Relationship};
}

interface Test extends T {
    relationships: {
        dcs: Relationship;
    };
}
</code></pre>

<p>The goal is for the relationships property in T to be an object with any number of keys that are all of the Relationship type. Test is supposed to be a specific implementation of type T.</p>

<p>Not sure what the correct way to approach this is. Thanks in advance!</p>