tripledoc/docs/writing-a-solid-app/3-reading-data.md

Library to read, create and update documents on a Solid Pod

---
id: 3-reading-data
title: Step 3: Reading data
---

We've [got the user's WebID](1-authentication) and we [know that it points to a
Document](2-understanding-solid); it's time we actually read some data from that Document!

We'll be using [Tripledoc](https://www.npmjs.com/package/tripledoc), which was designed
specifically for this purpose. Other libraries exist, such as
[ldflex](https://www.npmjs.com/package/ldflex), [rdf-ext](https://www.npmjs.com/package/rdf-ext) and
[rdflib](https://www.npmjs.com/package/rdflib); Tripledoc intentionally has a more limited scope, aimed to aid
"thinking in Solid". If at some point in the future you want to start combining many different
data sources, you might want to consider investigating these alternative libraries.

We'll try to get the user's name as follows:

1. Fetch the Document living at their WebID.
2. From that Document, read the Subject representing the current user's profile.
3. Get the `foaf:name` of that Subject, if set.

In code, that looks like this:

```typescript
import { fetchDocument } from 'tripledoc';

async function getName(webId) {
  /* 1. Fetch the Document at `webId`: */
  const webIdDoc = await fetchDocument(webId);
  /* 2. Read the Subject representing the current user's profile: */
  const profile = webIdDoc.getSubject(webId);
  /* 3. Get their foaf:name: */
  return profile.getString('http://xmlns.com/foaf/0.1/name')
}
```

Tip: you can avoid typing the full 'http://xmlns.com/foaf/0.1/name' every time using the library
[rdf-namespaces](https://www.npmjs.com/package/rdf-namespaces). It exports strings for the URLs of
the terms in common Vocabularies, turning the above into:

```typescript
import { fetchDocument } from 'tripledoc';
import { foaf } from 'rdf-namespaces';

async function getName(webId) {
  /* 1. Fetch the Document at `webId`: */
  const webIdDoc = await fetchDocument(webId);
  /* 2. Read the Subject representing the current user's profile: */
  const profile = webIdDoc.getSubject(webId);
  /* 3. Get their foaf:name: */
  return profile.getString(foaf.name)
}
```

Two things to note here. First, we call `getString` to indicate that we are looking for an actual
value (i.e. a Literal), rather than a URL. (Likewise, we could use `getInteger` or `getDecimal`
if we expected a number instead.) However, the value could also have been a URL pointing to a different
Subject, in which case we could in turn fetch _that_ Document. If that was what we expected, we
could have used the method `getRef` instead.

The second thing to consider is that we cannot make any assumptions about what data is, or is not,
present in the user's Pod. Thus, `profile.getString(foaf.name)` might also return `null`. This
could happen if the Document does not include the user's name, if the name is stored differently
(e.g. using `foaf:firstName` and `foaf:familyName`), or the value of `foaf:name` is not a literal string.

Now that we're able to read data from the user's WebID, let's find out how we can read arbitrary
other data.