import ballerina/io;

type Employee record {|
    readonly int id;
    string firstName;
    string lastName;
    int salary;
|};

public function main() {
    table<Employee> key(id) employees = table [
        {id: 1, firstName: "John", lastName: "Smith", salary: 100},
        {id: 2, firstName: "Jane", lastName: "Smith", salary: 150},
        {id: 4, firstName: "Fred", lastName: "Bloggs", salary: 200},
        {id: 7, firstName: "Bobby", lastName: "Clark", salary: 300},
        {id: 9, firstName: "Cassie", lastName: "Smith", salary: 250}
    ];

    // The `from` clause iterates the `employees` table.
    // Since the contextually-expected type for the query expression is `int[]` evaluation of the query expression will result in an integer array.
    int[] salaries = from var {salary} in employees
                     select salary;


    io:println(salaries);

    // The `from` clause iterates `employees` `table` and creates a `table`.
    // The query expression creates a `table` based on the contextually-expected type.
    table<Employee> smiths = from Employee emp in employees
                     where emp.lastName == "Smith" select emp;

    foreach Employee emp in smiths {
        io:println(emp.firstName, " ", emp.lastName);
    }
}

Querying tables

Tables can be nicely combined with query expressions unlike maps. Basic type of the output of query expression is determined by the contextually expected type and the input type.

 
import ballerina/io;

type Employee record {|
    readonly int id;
    string firstName;
    string lastName;
    int salary;
|};

public function main() {
    table<Employee> key(id) employees = table [
        {id: 1, firstName: "John", lastName: "Smith", salary: 100},
        {id: 2, firstName: "Jane", lastName: "Smith", salary: 150},
        {id: 4, firstName: "Fred", lastName: "Bloggs", salary: 200},
        {id: 7, firstName: "Bobby", lastName: "Clark", salary: 300},
        {id: 9, firstName: "Cassie", lastName: "Smith", salary: 250}
    ];

    int[] salaries = from var {salary} in employees
                     select salary;

The from clause iterates the employees table. Since the contextually-expected type for the query expression is int[] evaluation of the query expression will result in an integer array.

    io:println(salaries);

    table<Employee> smiths = from Employee emp in employees
                     where emp.lastName == "Smith" select emp;

The from clause iterates employees table and creates a table. The query expression creates a table based on the contextually-expected type.

    foreach Employee emp in smiths {
        io:println(emp.firstName, " ", emp.lastName);
    }
}

bal run querying_tables.bal
[100,150,200,300,250]
John Smith
Jane Smith
Cassie Smith