4. Relation Filling (FillDataChain)

Sometimes you have a list of objects obtained from an external source (like Redis, or a manual MyBatis XML query) and you want to populate their @ToOne or @ToMany relationships without writing a loop. FillDataChain solves this efficiently.

Entry Point: dataManager.fillChain()

// Assume we got this list from Redis, so 'department' field is null
List<User> users = cacheService.getUsers(); 

userService.fillChain()
    .data(users) // The targets to populate

    // 1. Simple fill: Populates the 'department' field
    .fillField("department")

    // 2. Complex fill: Populates 'roles', but only specific columns
    .fillField("roles", fieldBuilder -> {
        fieldBuilder.selectField("roleName") // Only fetch name
                    .selectField("roleCode");
    })

    .exec();

// Now 'users' have their department and roles populated.

---