John Gill Commentary 2 Samuel 12:29

"And David gathered all the people together, and went to Rabbah, and fought against it, and took it." — 2 Samuel 12:29 (ASV)

And David gathered all the people together
The soldiers that were with him, or near him; which was done partly to recruit Joab's troops, who, by the continuance of the siege, and the sallies of the enemy on them, might be greatly diminished; and partly to make conquests of other cities of the Ammonites, and to carry off the spoil of them:

and went to Rabbah ;
which must be after the death of Uriah, and very probably during the time of Bathsheba's mourning for him:

and fought against it, and took it ;
by assault.