mysqli - why is this php variable undefined -

Can anyone tell me why this does not work.

  class class1 {Private $ database; Function class1 () {$ database = $ this- & gt; Connect (); } Private Function Connect () {$ database = mysqli_connect ("localhost", "user name", "", "db"); If (mysqli_connect_errno ()) {echo "failed to connect to MySQL:". Mysqli_connect_error (); } $ Returned the database; } Private function usedb () {$ query = "Some SQL"; Mysqli_query ($ database, query $); }}   
 I hope this simple example can clearly demonstrate my problem adequately. Anyway, when I run something like this, I see an error that tells me that the "ezardb ()" function references an undefined variable "database". As if out of the scope of the variable ... can anyone give me a solution?  
 
 This is because in  class1 ()  you can add another local variable < Via code> $ databases :  
  $ database = $ this- & gt; Connect ();   
 To set and access the  $ database  property you should use:  
  $ this- & Gt; Database = $ this- & gt; Connect ();   
 same   function:  
  Personal function is used () {$ query = "some sql"; Mysqli_query ($ this- & gt; database, $ query); }   
 So your last code should look like this:  
  class class1 {Private $ database; Function class1 () {$ this-> Database = $ this- & gt; Connect (); } Private Function Connect () {$ database = mysqli_connect ("localhost", "user name", "", "db"); If (mysqli_connect_errno ()) {echo "failed to connect to MySQL:". Mysqli_connect_error (); } $ Returned the database; } Private function usedb () {$ query = "Some SQL"; Mysqli_query ($ this- & gt; database, $ query); }}   
  Note:   
 The same applies to  $ databases  in  connectivity ( )  function. Although with the same name, it does not do anything with the  $ database  variable outside, because it should be used for  $ this-> database  (if necessary)