CHORD SCALE THEAORY
Every chord in music has its Parent Scale, take for example a C major chord which is CEG i.e. d m s
Is derived from the major scale or tonic sol-fa which drmfsltd the C major Scale is the 1st , 3rd and 5th of the major Scale.
Scale                               C             D                   E              F                    G             A                   B
Notes of the scale        D             r                    m              f                     s             l                     t  
Scale degree                 Root      2nd or 9th    3rd    4th or 11th       5th         6th or 13th     7th
The chord extension are extra not added to the chord from the parent scale choice, so a Cmaj7th chord is a C major  chord with the 7th from the scale added to it which is B or t
Cmaj7th     =     C    E    G    B
                            1   3     5     7
There given a Cmaj7th chord you can play a C major scale over it.

Cmaj9th =      C    E    G    B    D
                          1    3    5    7    2
Notice that the Cmaj9th has two extension added to the C major scale from the major scale, which are the 7th or B and the 9th or D.

For a minor chord which is made up of the root, flat 3 and 5th of the parent scale, the scale choice will be dependent on the quality of the chord. For a C minor chord you can use a Cmin scale which is   CDEBFGAbBbC   ltdrmfsl
Cmin scale     =     C    D    Eb   F    G    Ab      Bb
C min             =     C           Eb         G                    
                               1            3            5
                        =     C    D    Eb   F    G    Ab      Bb
 Cmin7            =     C            Eb          G             Bb      
                               1              3            5                 7