to have no choice but to

• 出于不得已

  born of necessity

• 在不得已的时候

  when one has no alternative

• 不得已的措施

  measure of last resort

• 不得已而为之

  had no choice but to do so

• 不得已而求其次

  have to settle for second best

• 我不得已而同意了。

  I had no choice but to agree.