Add Grab Values From An Array Of References as a GROQ til

groq/grab-values-from-an-array-of-references.md

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+# Grab Values From An Array Of References
+
+Let's say we have a `post` object in our schema. A `post` can have an array of
+references to `tags` telling you what topics the post covers. Each `tag` has a
+slug and we want to get the `string` value for each slug.
+
+Let's say we are interested in the post with `_id` of `123`.
+
+Here is how we can achieve that with a `groq` query:
+
+```groq
+*[
+  _type == 'post' && _id == 123
+]{
+  'tags': tags[]->slug.current
+}.tags
+
+=> ["javascript", "react-js"]
+```
+
+If the schema was such that each `post` just had a single tag reference, then
+you could write the chain of references as `tag->slug.current`. Because it is
+an array of references, we need the `[]` to declare that we want each value.
+
+The `->` operator follows the reference. Otherwise we'd just have access to the
+`_ref` and `_type` values.
+
+The final `.tags` unnests the `tags` value we gathered into an object. Then the
+result is just the array of slug values.