Module sql
ballerina/sql Ballerina library
Overview
This module provides the common interface and functionality to interact with a database. The corresponding database
clients can be created by using specific database modules such as mysql
or using the Java Database Connectivity
module jdbc
.
List of Database Modules
Ballerina now has the jdbc
module as the generic DB connector module to connect to any relational database by simply providing the JDBC URL and the other related properties.
Ballerina also provides specially designed various database-specific DB connectors so that you can work with different databases and you can access their DB-specific functionalities.
Client
The database client should be created using any of the above-listed database modules and once it is created, the operations and functionality explained below can be used.
Connection Pool Handling
All database modules share the same connection pooling concept and there are three possible scenarios for
connection pool handling. For its properties and possible values, see the sql:ConnectionPool
.
-
Global, shareable, default connection pool
If you do not provide the
poolOptions
field when creating the database client, a globally-shareable pool will be created for your database unless a connection pool matching with the properties you provided already exists. The JDBC module example below shows how the global connection pool is used.jdbc:Client|sql:Error dbClient = new ("jdbc:mysql://localhost:3306/testdb", "root", "root");
-
Client-owned, unsharable connection pool
If you define the
connectionPool
field inline when creating the database client with thesql:ConnectionPool
type, an unsharable connection pool will be created. The JDBC module example below shows how the global connection pool is used.jdbc:Client|sql:Error dbClient = new (url = "jdbc:mysql://localhost:3306/testdb", connectionPool = { maxOpenConnections: 5 });
-
Local, shareable connection pool
If you create a record of the
sql:ConnectionPool
type and reuse that in the configuration of multiple clients, for each set of clients that connects to the same database instance with the same set of properties, a shared connection pool will be created. The JDBC module example below shows how the global connection pool is used.sql:ConnectionPool connPool = {maxOpenConnections: 5}; jdbc:Client|sql:Error dbClient1 = new (url = "jdbc:mysql://localhost:3306/testdb", connectionPool = connPool); jdbc:Client|sql:Error dbClient2 = new (url = "jdbc:mysql://localhost:3306/testdb", connectionPool = connPool); jdbc:Client|sql:Error dbClient3 = new (url = "jdbc:mysql://localhost:3306/testdb", connectionPool = connPool);
Closing the Client
Once all the database operations are performed, you can close the database client you have created by invoking the close()
operation. This will close the corresponding connection pool if it is not shared by any other database clients.
error? e = dbClient.close();
Or
check dbClient.close();
Database Operations
Once the client is created, database operations can be executed through that client. This module defines the interface and common properties that are shared among multiple database clients. It also supports querying, inserting, deleting, updating, and batch updating data.
Creating Tables
This sample creates a table with two columns. One column is of type int
and the other is of type varchar
.
The CREATE
statement is executed via the execute
remote function of the client.
// Create the ‘Students’ table with the ‘id’, 'name', and ‘age’ fields. sql:ExecutionResult ret = check dbClient->execute("CREATE TABLE student(id INT AUTO_INCREMENT, " + "age INT, name VARCHAR(255), PRIMARY KEY (id))"); //A value of the sql:ExecutionResult type is returned for 'ret'.
Inserting Data
This sample shows three examples of data insertion by executing an INSERT
statement using the execute
remote function
of the client.
In the first example, the query parameter values are passed directly into the query statement of the execute
remote function.
sql:ExecutionResult ret = check dbClient->execute("INSERT INTO student(age, name) " + "values (23, 'john')");
In the second example, the parameter values, which are in local variables are used to parameterize the SQL query in
the execute
remote function. This type of a parameterized SQL query can be used with any primitive Ballerina type
like string
, int
, float
, or boolean
and in that case, the corresponding SQL type of the parameter is derived
from the type of the Ballerina variable that is passed in.
string name = "Anne"; int age = 8; sql:ParameterizedQuery query = `INSERT INTO student(age, name) values (${age}, ${name})`; sql:ExecutionResult ret = check dbClient->execute(query);
In the third example, the parameter values are passed as a sql:TypedValue
to the execute
remote function. Use the
corresponding subtype of the sql:TypedValue
such as sql:Varchar
, sql:Char
, sql:Integer
, etc., when you need to
provide more details such as the exact SQL type of the parameter.
sql:VarcharValue name = new ("James"); sql:IntegerValue age = new (10); sql:ParameterizedQuery query = `INSERT INTO student(age, name) values (${age}, ${name})`; sql:ExecutionResult ret = check dbClient->execute(query);
Inserting Data With Auto-generated Keys
This example demonstrates inserting data while returning the auto-generated keys. It achieves this by using the
execute
remote function to execute the INSERT
statement.
int age = 31; string name = "Kate"; sql:ParameterizedQuery query = `INSERT INTO student(age, name) values (${age}, ${name})`; sql:ExecutionResultret = check dbClient->execute(query); //Number of rows affected by the execution of the query. int? count = ret.affectedRowCount; //The integer or string generated by the database in response to a query execution. string|int? generatedKey = ret.lastInsertId; }
Querying Data
This sample shows three examples to demonstrate the different usages of the query
operation to query the
database table and obtain the results.
This example demonstrates querying data from a table in a database.
First, a type is created to represent the returned result set. Note the mapping of the database column
to the returned record's property is case-insensitive (i.e., the ID
column in the result can be mapped to the id
property in the record). Next, the SELECT
query is executed via the query
remote function of the client by passing that
result set type. Once the query is executed, each data record can be retrieved by looping the result set. The stream
returned by the select operation holds a pointer to the actual data in the database and it loads data from the table
only when it is accessed. This stream can be iterated only once.
// Define a type to represent the results. type Student record { int id; int age; string name; }; // Select the data from the database table. The query parameters are passed // directly. Similar to the `execute` examples, parameters can be passed as // sub types of `sql:TypedValue` as well. int id = 10; int age = 12; sql:ParameterizedQuery query = `SELECT * FROM students WHERE id < ${id} AND age > ${age}`; stream<Student, sql:Error> resultStream = <stream<Student, sql:Error>> dbClient->query(query, Student); // Iterating the returned table. error? e = resultStream.forEach(function(Student student) { //Can perform any operations using 'student' and can access any fields in the returned record of type Student. });
Defining the return type is optional and you can query the database without providing the result type. Hence, the above example can be modified as follows with an open record type as the return type. The property name in the open record type will be the same as how the column is defined in the database.
// Select the data from the database table. The query parameters are passed // directly. Similar to the `execute` examples, parameters can be passed as // sub types of `sql:TypedValue` as well. int id = 10; int age = 12; sql:ParameterizedQuery query = `SELECT * FROM students WHERE id < ${id} AND age > ${age}`; stream<record{}, sql:Error> resultStream = dbClient->query(query); // Iterating the returned table. error? e = resultStream.forEach(function(record{} student) { //Can perform any operations using the 'student' and can access any fields in the returned record. });
There are situations in which you may not want to iterate through the database and in that case, you may decide
to only use the next()
operation in the result stream
and retrieve the first record. In such cases, the returned
result stream will not be closed, and you have to explicitly invoke the close
operation on the
sql:Client
to release the connection resources and avoid a connection leak as shown below.
stream<record{}, sql:Error> resultStream = dbClient->query("SELECT count(*) as total FROM students"); record {|record {} value;|}|error? result = resultStream.next(); if result is record {|record {} value;|} { // A valid result is returned. } else if result is error { // An error is returned as the result. } else { // Student table must be empty. } error? e = resultStream.close();
Updating Data
This example demonstrates modifying data by executing an UPDATE
statement via the execute
remote function of
the client.
int age = 23; sql:ParameterizedQuery query = `UPDATE students SET name = 'John' WHERE age = ${age}`; sql:ExecutionResult|sql:Error ret = check dbClient->execute(query);
Deleting Data
This example demonstrates deleting data by executing a DELETE
statement via the execute
remote function of
the client.
string name = "John"; sql:ParameterizedQuery query = `DELETE from students WHERE name = ${name}`; sql:ExecutionResult|sql:Error ret = check dbClient->execute(query);
Batch Updating Data
This example demonstrates how to insert multiple records with a single INSERT
statement that is executed via the
batchExecute
remote function of the client. This is done by creating a table
with multiple records and
parameterized SQL query as same as the above execute
operations.
// Create the table with the records that need to be inserted. var data = [ { name: "John", age: 25 }, { name: "Peter", age: 24 }, { name: "jane", age: 22 } ]; // Do the batch update by passing the batches. sql:ParameterizedQuery[] batch = from var row in data select `INSERT INTO students ('name', 'age') VALUES (${row.name}, ${row.age})`; sql:ExecutionResult[] ret = check dbClient->batchExecute(batch);
Execute SQL Stored Procedures
This example demonstrates how to execute a stored procedure with a single INSERT
statement that is executed via the
call
remote function of the client.
int uid = 10; sql:IntegerOutParameter insertId = new; sql:ProcedureCallResult|sql:Error ret = dbClient->call(`call InsertPerson(${uid}, ${insertId})`); if ret is error { //An error returned. } else { stream<record{}, sql:Error>? resultStr = ret.queryResult; if resultStr is stream<record{}, sql:Error> { sql:Error? e = resultStr.forEach(function(record{} result) { //can perform operations using 'result'. }); } check ret.close(); }
Note that you have to invoke the close operation explicitly on the sql:ProcedureCallResult
to release the connection resources and avoid a connection leak as shown above.
Note: The default thread pool size used in Ballerina is: [the number of processors available * 2] . You can configure the thread pool size by using the
BALLERINA_MAX_POOL_SIZE
environment variable.