As we mentioned in the previous section, database sets and maps are two types of collections that allows the organization of multiple instances of data in the database. We can query a set of values using the following operators:
== expr: equals expr != expr: not equals expr < expr: lesser than expr <= expr: lesser than or equals expr > expr: greater than expr >= expr: greater than or equals expr in expr: "belongs to" expr, where expr is a list q1 or q2: satisfy query q1 or q2 q1 and q2: satisfy both queries, q1 and q2 not q: does not satisfy q {f1 q1, f2 q2, ...}: the database field f1 satisfies q1, field f2 satisfies q2 etc.
Furthermore, we can specify some querying options as follows:
skip n: Hereexprshould be an expression of typeintand it skip the first n results.limit n: Hereexprshould be an expression of typeint, returns a maximum of n results.order fld (, fld)+: Herefldspecifies an order.fldcan be a single identifier or a list of identifiers...