What is Lazy Loading?

Question

What is Lazy Loading?

[Edit after reading a few answers] Why do people use this term so often?

Say you just use a ASP/ADO recordset and load it with data or

Answer 1

The term lazy loading is usually used when talking about object relational mappers. If you use ADO.NET directly you always get eager loading (ie it always loads just what you specify).

OR-mappers like nHibernate support returning proxy objects that get "filled in" with the right data only when you access the data. That way you only load the data that you really use. This is a usefull feature when you specify a lot of relations between objects that can get loaded from the database, you don't want the OR-mapper to load all the related objects and the objects related to the related objects and so on. That can result in your whole database getting loaded.

This problem can be prevented by carefull design of your object model too. (using aggregates and only loading aggregate roots like in domain driven design is a way to get around this without using lazy loading).

Lazy loading can result in the or mapper doing lots of small database accesses instead of retrieving all the data you need once. This can result in performance problems too.

Answer 2

An example of Lazy Loading would be a grid or table with lots of data on a webpage to view where the application only loads what the users browser viewpoint size is at that time. When they scroll down to want to view more content or data, more data would be loaded into view at that moment.

This is becoming more of a common visual/interaction design pattern as well via ajax or jQuery.

And as mentioned above, opposite would be Eager Loading where you don't take client into consideration thus potentially having a performance hit.

Answer 3

According to geeksforgeeks, Lazy loading is a software design pattern where the initialization of an object occurs only when it is actually needed and not before to preserve the simplicity of usage and improve performance.

https://www.geeksforgeeks.org/lazy-loading-design-pattern/

Answer 4

Lazy<T> is now part of c# 4.0 - there is a nice page on MSDN which explains the concept.

Answer 5

wikipedia's Definition Lazy loading is a design pattern commonly used in computer programming to defer initialization of an object until the point at which it is needed. ...

http://en.wikipedia.org/wiki/Lazy%20loading

Answer 6

Lazy loading: you don't waste your time (nor your memory) with stuff you might not need. Then when you need it, it takes longer, but that's fine.

Example from life: instead of actually learning that French phrasebook, you learn the phrases one at a time, as they're needed. When does this make sense? If you're only going to be in France for a short time (i.e., you won't need a lot of the phrases) or if you need to leave very soon. If you're there for two years and/or you have a long time to study, then it might be much more efficient to just learn the whole phrasebook up front (eager loading).

[Inspired by the Atom as taught in gang terms by Venus on WKRP.]