Figure 44. ObjectLookup

The simplest way to navigate in an object is similar to JavaScript, using a dot. This will work as soon as you do not push it too much: alphanumerical characters, dashes, underscores - just like unquoted keys in object constructors, any NCName is allowed.

{ "foo" : "bar" }.foo
      

Since JSONiq expressions are composable, you can also use any expression for the left-hand side. You might need parentheses depending on the precedence.

collection("one-object").foo
      

The dot operator does an implicit mapping on the left-hand-side, i.e., it applies the lookup in turn on each item. Lookup on an object returns the value associated with the supplied key, or the empty sequence if there is none. Lookup on any item which is not an object (arrays and atomics) results in the empty sequence.

({ "foo" : "bar" }, { "foo" : "bar2" }, { "bar" : "foo" }).foo
        

collection("captains").name
      

({ "foo" : "bar1" }, [ "foo", "bar" ], { "foo" : "bar2" }, "foo").foo
      

Of course, unquoted keys will not work for strings that are not NCNames, e.g., if the field contains a dot or begins with a digit. Then you will need quotes.

{ "foo bar" : "bar" }."foo bar"
      

If you use an expression on the right side of the dot, it must always have parentheses. The result of the right-hand-side expression is cast to a string. An error is raised if the cast fails.

{ "foobar" : "bar" }.("foo" || "bar")
      

{ "foobar" : "bar" }.("foo", "bar")
      

{ "1" : "bar" }.(1)
      

Variables, or a context item reference, do not need parentheses. Variables are introduced later, but here is a sneak peek:

let $field := "foo" || "bar"
return { "foobar" : "bar" }.$field