我有两个问题。

1.方案中没有类别对应的joinable!条目，为什么会出现这种情况？
1.如果添加了两列外键引用到同一表，则不允许手动添加两条joinable!语句，例如：

joinable!(categories -> users (created_by));
joinable!(categories -> users (modified_by));

我尝试使用一个指向“USERS”表的外键引用来创建“Categories”表，删除了数据库、删除了方案、运行了迁移，但仍然没有更改方案。

table! {
    categories (id) {
        id -> Int4,
        category_code -> Varchar,
        description -> Varchar,
        gl_cr -> Varchar,
        gl_dr -> Varchar,
        asset_cost_less_than -> Nullable<Int4>,
        over_ride_depreciation_rate -> Bool,
        over_ride_useful_life -> Bool,
        created_by -> Int4,
        created_on -> Timestamp,
        modified_by -> Nullable<Int4>,
        modified_date -> Nullable<Timestamp>,
    }
}

table! {
    users (id) {
        id -> Int4,
        username -> Varchar,
        full_name -> Varchar,
        email -> Varchar,
        active -> Bool,
        created_on -> Timestamp,
    }
}

架构的一部分。Rs是

joinable!(branch_categories -> categories (category_id));
joinable!(branches -> cities (city_id));
joinable!(branches -> users (created_by));
joinable!(category_book_rate_codes -> books (book_id));
joinable!(category_book_rate_codes -> categories (category_id));
joinable!(category_book_rate_codes -> depreciation_rates (rate_id));
joinable!(cities -> states (state_id));
joinable!(cities -> users (created_by));