Analysis of the $ db-> where () chain principle in the codeigniter framework

The most common framework in the company is codeigniter, which is frequently used.

$ Db-> select ()-> from ()-> where ()

Some new users may find this statement strange. How is this implemented ????

In fact, the principle is relatively simple. Let's give an example and you will understand it.

Class demo {
Public $ SQL = "";
Function select ($ str)
 {
$ This-> SQL. = $ str;
Return $ this;
 }
Function from ($ str)
 {
$ This-> SQL. = $ str;
Return $ this;
 }
Function where ($ str)
 {
$ This-> SQL. = $ str;
Return $ this;
 }
Function query ()
 {
Execute ....
Return array
 }
}

In fact, the key is that every time a chained function returns an object's own reference, it will then call its own function !! Until the end of the query function!