Suppose that we wish store a set of phone numbers for a user each identified by a category of phone type, such as home phone or office phone. We can do this by using a map where the key is phone type and value can be a set of phone numbers, assuming there are multiple phone numbers of each type. This is an example of nested collection where we are using a set as value within a map. Let us try to create the collection:
ALTER TABLE "users"
ADD "telephone_numbers" map<text, set<text>>;You will get an error saying non-frozen collections are not allowed inside collections:
Cassandra lets us use nested collection types only if we use the frozen collections nested within the frozen or non-frozen collections. This means we cannot update individual values of the frozen collection. To create the preceding collection, use this:
ALTER TABLE "users"
ADD "telephone_numbers" map<text, frozen<set<text>>>;
Now let's add some home as well as office phone numbers...