Basic migration skeleton

migrate.rs

const CONTRACT_NAME: &str = "crates.io:my-crate-name";
const CONTRACT_VERSION: &str = env!("CARGO_PKG_VERSION");

#[entry_point]
pub fn migrate(deps: DepsMut, _env: Env, msg: MigrateMsg) -> Result<Response, ContractError> {
    let ver = cw2::get_contract_version(deps.storage)?;
    // ensure we are migrating from an allowed contract
    if ver.contract != CONTRACT_NAME {
        return Err(StdError::generic_err("Can only upgrade from same type").into());
    }
    // note: better to do proper semver compare, but string compare *usually* works
    if ver.version >= CONTRACT_VERSION {
        return Err(StdError::generic_err("Cannot upgrade from a newer version").into());
    }
    
    // set the new version
    cw2::set_contract_version(deps.storage, CONTRACT_NAME, CONTRACT_VERSION)?;
    
    // do any desired state migrations...
    
    Ok(Response::default())
}