Account Constraints

Constraint Macros

Anchor validates accounts before your instruction logic runs. If any constraint fails, the transaction reverts.

Common Constraints

#[derive(Accounts)]
pub struct Enroll<'info> {
    // PDA derivation + initialization
    #[account(
        init,
        payer = learner,
        space = 8 + Enrollment::INIT_SPACE,
        seeds = [b"enrollment", course.course_id.as_bytes(), learner.key().as_ref()],
        bump,
    )]
    pub enrollment: Account<'info, Enrollment>,

    // Read-only, validate it's active
    #[account(constraint = course.is_active @ ErrorCode::CourseNotActive)]
    pub course: Account<'info, Course>,

    // Must be a signer and mutable (pays rent)
    #[account(mut)]
    pub learner: Signer<'info>,

    pub system_program: Program<'info, System>,
}

Constraint Types

• `init` — create and initialize the account

• `mut` — account must be writable

• `seeds` + `bump` — PDA derivation and verification

• `has_one` — field must match another account's key

• `constraint` — arbitrary boolean expression

• `close` — close account and return lamports

• `realloc` — resize account data