####1.About how to remove a foreign key in a table(MySQL):

1. a, find the constraint: show create table TABLE_NAME; From this request you can see the CONSTRAINt of the foreign key, it’s a sequence like “FK84229236324DD57”

2. b, alter table user_radius_attribute drop foreign key FK84229236324DD57 this command removes the foreign key

3. c, if removing a primary key, the command is alter table user_radius_attribute drop key FK84229236324DD57

####2. ExtJs Array different method comparing

Extjs has a few methods to loop an Array, which are quite similar yet still have differences.

forEach(): loop the whole elements of the array, just like for-loop

every(): loop the whole elements of the array, but stops looping the first time the iterator returns false or something falsy

some(): loops and stops looping the first time the iterator returns true or something truthy

filter(): creates a new array including elements where the filter function returns true and omitting the ones where it returns false

map(): creates a new array from the values returned by the iterator function

reduce(): builds up a value by repeated calling the iterator, passing in previous values; see the spec for the details; useful for summing the contents of an array and many other things

reduceRight(): like reduce, but works in descending rather than ascending order

1. d, The way grails to avoid the xss attack:

	<g:encodeAs codec="HTML"> 
	 ${a.token.description}
	</g:encodeAs>

encode the content as html so that the browser will render it instead of judging it as javascript.

1. e, <meta content="width=device-width, initial-scale=1.0" name="viewport"/> This sentence in html file tells browser to adjust width just to comply with the screen width.