Book Image

Opa Application Development

By : Li Wenbo
Book Image

Opa Application Development

By: Li Wenbo

Overview of this book

Opa is a full-stack Open Source web development framework for JavaScript that lets you write secure and scalable web applications. It generates standard Node.js/MongoDB applications, natively supports HTML5 and CSS and automates many aspects of modern web application programming. It handles all aspects of web programming written in one consistent language and compiled to web standards.Opa Application Development is a practical,hands-on guide that provides you with a number of step-by-step exercises. It covers almost all aspects of developing a web application with Opa, which will help you take advantage of the real power of Opa, as well as building a secure, powerful web application rapidly.Opa Application Development dives into all concepts and components required to build a web application with Opa. The first half of this book shows you all of the basic building blocks that you will need to develop an Opa application, including the syntax of Opa, web development aspects, client and server communication and slicing, plugin, database, and so on. By the end of the book you will have yourself created a complete web application along with a game: Pacman!
Table of Contents (18 chapters)
Opa Application Development
About the Author
About the Reviewers

Querying data

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: Here expr should be an expression of type int and it skip the first n results.

  • limit n: Here expr should be an expression of type int, returns a maximum of n results.

  • order fld (, fld)+: Here fld specifies an order. fld can be a single identifier or a list of identifiers...