diff options
| -rw-r--r-- | view/driver.cxx | 22 | ||||
| -rw-r--r-- | view/employee.hxx | 18 |
2 files changed, 40 insertions, 0 deletions
diff --git a/view/driver.cxx b/view/driver.cxx index 74d6eed..d975cc4 100644 --- a/view/driver.cxx +++ b/view/driver.cxx @@ -314,6 +314,28 @@ main (int argc, char* argv[]) t.commit (); } + // Get the list of employers that have any employees. + // + { + typedef odb::result<employer_with_employees> result; + + shared_ptr<employer> es (new employer (3, "Empty Shell LLC")); + + transaction t (db->begin ()); + db->persist (es); + + result r (db->query<employer_with_employees> ()); + + cout << "Employers with employees" << endl; + + for (result::iterator i (r.begin ()); i != r.end (); ++i) + cout << " " << i->e->name () << endl; + + cout << endl; + + db->erase (es); + t.commit (); + } // Get the list of employees that have accumulated vacation days. // diff --git a/view/employee.hxx b/view/employee.hxx index 87f0bce..4e1b745 100644 --- a/view/employee.hxx +++ b/view/employee.hxx @@ -253,6 +253,24 @@ struct employee_country_objects shared_ptr<country> nat; }; +// An example of using inner join type. Here we want to find employers +// that have any employees. If we were to use the default left join type, +// then we would have gotten all the employers, regardless of whether +// they have any employees. By using the inner join, we make sure that +// only matching employers are returned. +// +// It is also likely that there will be more than one employee for any +// particular employer which will lead to duplicate employer records +// being returned. To avoid this we use the 'distinct' result modifier. +// +// Try to change the join type or remove 'distinct' to observe the +// change in behavior. +// +#pragma db view object(employer) object(employee inner) query(distinct) +struct employer_with_employees +{ + shared_ptr<employer> e; +}; // An example of a native view that provides a complete query and is based // on an ad-hoc table. This view allows us to load the employee vacation |