== Vert.x Common SQL interface

The common SQL interface is used to interact with Vert.x SQL services.

You obtain a connection to the database via the service interface for the specific SQL service that
you are using (e.g. JDBC/MySQL/PostgreSQL).

To use this project, add the following dependency to the _dependencies_ section of your `module.ceylon`:

[source,xml,subs="+attributes"]
----
shared import io.vertx.ceylon.sql "3.3.2";
----

== The SQL Connection

A connection to the database is represented by `link:../../ceylondoc/vertx-sql//SQLConnection.type.html[SQLConnection]`.

=== Auto-commit

When you obtain a connection auto commit is set to `true`. This means that each operation you perform will effectively
execute in its own transaction.

If you wish to perform multiple operations in a single transaction you should set auto commit to false with
`link:../../ceylondoc/vertx-sql//SQLConnection.type.html#setAutoCommit(boolean,%20io.vertx.core.Handler)[setAutoCommit]`.

When the operation is complete, the handler will be called:

[source,java]
----
connection.setAutoCommit(false, (Throwable? res) {
  if (!exists res) {
    // OK!
  } else {
    // Failed!
  };
});

----

=== Executing queries

To execute a query use `link:../../ceylondoc/vertx-sql//SQLConnection.type.html#query(java.lang.String,%20io.vertx.core.Handler)[query]`

The query string is raw SQL that is passed through without changes to the actual database.

The handler will be called with the results, represented by `link:../../ceylondoc/vertx-sql//ResultSet.type.html[ResultSet]` when the query has
been run.

[source,java]
----
connection.query("SELECT ID, FNAME, LNAME, SHOE_SIZE from PEOPLE", (ResultSet|Throwable res) {
  if (is ResultSet res) {
    // Get the result set
    value resultSet = res;
  } else {
    // Failed!
  };
});

----

The `link:../../ceylondoc/vertx-sql//ResultSet.type.html[ResultSet]` instance represents the results of a query.

The list of column names are available with `link:../../ceylondoc/vertx-sql//ResultSet.type.html#getColumnNames()[getColumnNames]`, and the actual results
available with `link:../../ceylondoc/vertx-sql//ResultSet.type.html#getResults()[getResults]`

The results are a list of `JsonArray` instances, one for each row of the results.

[source,java]
----

value columnNames = resultSet.columnNames;

value results = resultSet.results;

for (row in results) {

  value id = row[0];
  value fName = row[1];
  value lName = row[2];
  value shoeSize = row[3];

};


----

You can also retrieve the rows as a list of Json object instances with `link:../../ceylondoc/vertx-sql//ResultSet.type.html#getRows()[getRows]` -
this can give you a somewhat simpler API to work with, but please be aware that SQL results can contain duplicate
column names - if that's the case you should use `link:../../ceylondoc/vertx-sql//ResultSet.type.html#getResults()[getResults]` instead.

Here's an example of iterating through the results as Json object instances:

[source,java]
----

value rows = resultSet.rows;

for (row in rows) {

  value id = rowget("ID";
  value fName = rowget("FNAME";
  value lName = rowget("LNAME";
  value shoeSize = rowget("SHOE_SIZE";

};


----

=== Prepared statement queries

To execute a prepared statement query you can use
`link:../../ceylondoc/vertx-sql//SQLConnection.type.html#queryWithParams(java.lang.String,%20io.vertx.core.json.JsonArray,%20io.vertx.core.Handler)[queryWithParams]`.

This takes the query, containing the parameter place holders, and a `JsonArray` or parameter
values.

[source,java]
----

value query = "SELECT ID, FNAME, LNAME, SHOE_SIZE from PEOPLE WHERE LNAME=? AND SHOE_SIZE > ?";
value params = JsonArray {"Fox" , 9 };

connection.queryWithParams(query, params, (ResultSet|Throwable res) {

  if (is ResultSet res) {
    // Get the result set
    value resultSet = res;
  } else {
    // Failed!
  };
});


----

=== Executing INSERT, UPDATE or DELETE

To execute an operation which updates the database use `link:../../ceylondoc/vertx-sql//SQLConnection.type.html#update(java.lang.String,%20io.vertx.core.Handler)[update]`.

The update string is raw SQL that is passed through without changes to the actual database.

The handler will be called with the results, represented by `link:../../ceylondoc/vertx-sql//UpdateResult.type.html[UpdateResult]` when the update has
been run.

The update result holds the number of rows updated with `link:../../ceylondoc/vertx-sql//UpdateResult.type.html#getUpdated()[getUpdated]`, and
if the update generated keys, they are available with `link:../../ceylondoc/vertx-sql//UpdateResult.type.html#getKeys()[getKeys]`.

[source,java]
----

connection.update("INSERT INTO PEOPLE VALUES (null, 'john', 'smith', 9)", (UpdateResult|Throwable res) {
  if (is UpdateResult res) {

    value result = res;
    print("Updated no. of rows: ``result.updated``");
    print("Generated keys: ``result.keys``");

  } else {
    // Failed!
  };
});



----

=== Prepared statement updates

To execute a prepared statement update you can use
`link:../../ceylondoc/vertx-sql//SQLConnection.type.html#updateWithParams(java.lang.String,%20io.vertx.core.json.JsonArray,%20io.vertx.core.Handler)[updateWithParams]`.

This takes the update, containing the parameter place holders, and a `JsonArray` or parameter
values.

[source,java]
----

value update = "UPDATE PEOPLE SET SHOE_SIZE = 10 WHERE LNAME=?";
value params = JsonArray {"Fox" };

connection.updateWithParams(update, params, (UpdateResult|Throwable res) {

  if (is UpdateResult res) {

    value updateResult = res;

    print("No. of rows updated: ``updateResult.updated``");

  } else {

    // Failed!

  };
});


----

=== Callable statements

To execute a callable statement (either SQL functions or SQL procedures) you can use
`link:../../ceylondoc/vertx-sql//SQLConnection.type.html#callWithParams(java.lang.String,%20io.vertx.core.json.JsonArray,%20io.vertx.core.json.JsonArray,%20io.vertx.core.Handler)[callWithParams]`.

This takes the callable statement using the standard JDBC format `{ call func_proc_name() }`, optionally including
parameter place holders e.g.: `{ call func_proc_name(?, ?) }`, a `JsonArray` containing the
parameter values and finally a `JsonArray` containing the
output types e.g.: `[null, 'VARCHAR']`.

Note that the index of the output type is as important as the params array. If the return value is the second
argument then the output array must contain a null value as the first element.

A SQL function returns some output using the `return` keyword, and in this case one can call it like this:

[source,java]
----
// Assume that there is a SQL function like this:
//
// create function one_hour_ago() returns timestamp
//    return now() - 1 hour;

// note that you do not need to declare the output for functions
value func = "{ call one_hour_ago() }";

connection.call(func, (ResultSet|Throwable res) {

  if (is ResultSet res) {
    value result = res;
  } else {
    // Failed!
  };
});

----

When working with Procedures you and still return values from your procedures via its arguments, in the case you do
not return anything the usage is as follows:

[source,java]
----
// Assume that there is a SQL procedure like this:
//
// create procedure new_customer(firstname varchar(50), lastname varchar(50))
//   modifies sql data
//   insert into customers values (default, firstname, lastname, current_timestamp);

value func = "{ call new_customer(?, ?) }";

connection.callWithParams(func, JsonArray {"John" , "Doe" }, null, (ResultSet|Throwable res) {

  if (is ResultSet res) {
    // Success!
  } else {
    // Failed!
  };
});

----

However you can also return values like this:

[source,java]
----
// Assume that there is a SQL procedure like this:
//
// create procedure customer_lastname(IN firstname varchar(50), OUT lastname varchar(50))
//   modifies sql data
//   select lastname into lastname from customers where firstname = firstname;

value func = "{ call customer_lastname(?, ?) }";

connection.callWithParams(func, JsonArray {"John" }, JsonArray {null , "VARCHAR" }, (ResultSet|Throwable res) {

  if (is ResultSet res) {
    value result = res;
  } else {
    // Failed!
  };
});

----

Note that the index of the arguments matches the index of the `?` and that the output parameters expect to be a
String describing the type you want to receive.

To avoid ambiguation the implementations are expected to follow the following rules:

* When a place holder in the `IN` array is `NOT NULL` it will be taken
* When the `IN` value is NULL a check is performed on the OUT
  * When the `OUT` value is not null it will be registered as a output parameter
  * When the `OUT` is also null it is expected that the IN value is the `NULL` value.

The registered `OUT` parameters will be available as an array in the result set under the output property.

=== Batch operations

The SQL common interface also defines how to execute batch operations. There are 3 types of batch operations:

* Batched statements `link:../../ceylondoc/vertx-sql//SQLConnection.type.html#batch(java.util.List,%20io.vertx.core.Handler)[batch]`
* Batched prepared statements `link:../../ceylondoc/vertx-sql//SQLConnection.type.html#batchWithParams(java.lang.String,%20java.util.List,%20io.vertx.core.Handler)[batchWithParams]`
* Batched callable statements `link:../../ceylondoc/vertx-sql//SQLConnection.type.html#batchCallableWithParams(java.lang.String,%20java.util.List,%20java.util.List,%20io.vertx.core.Handler)[batchCallableWithParams]`

A batches statement will exeucte a list of sql statements as for example:

[source,java]
----
// Batch values
value batch = renderNewList;
renderListAdd;
renderListAdd;

connection.batch(batch, (List<Integer>|Throwable res) {
  if (is List<Integer> res) {
    value result = res;
  } else {
    // Failed!
  };
});

----

While a prepared or callable statement batch will reuse the sql statement and take an list of arguments as for example:

[source,java]
----
// Batch values
value batch = renderNewList;
renderListAdd;
renderListAdd;

connection.batchWithParams("INSERT INTO emp (name) VALUES (?)", batch, (List<Integer>|Throwable res) {
  if (is List<Integer> res) {
    value result = res;
  } else {
    // Failed!
  };
});

----

=== Executing other operations

To execute any other database operation, e.g. a `CREATE TABLE` you can use
`link:../../ceylondoc/vertx-sql//SQLConnection.type.html#execute(java.lang.String,%20io.vertx.core.Handler)[execute]`.

The string is passed through without changes to the actual database. The handler is called when the operation
is complete

[source,java]
----

value sql = "CREATE TABLE PEOPLE (ID int generated by default as identity (start with 1 increment by 1) not null,FNAME varchar(255), LNAME varchar(255), SHOE_SIZE int);";

connection.execute(sql, (Throwable? execute) {
  if (!exists execute) {
    print("Table created !");
  } else {
    // Failed!
  };
});


----

=== Using transactions

To use transactions first set auto-commit to false with `link:../../ceylondoc/vertx-sql//SQLConnection.type.html#setAutoCommit(boolean,%20io.vertx.core.Handler)[setAutoCommit]`.

You then do your transactional operations and when you want to commit or rollback use
`link:../../ceylondoc/vertx-sql//SQLConnection.type.html#commit(io.vertx.core.Handler)[commit]` or
`link:../../ceylondoc/vertx-sql//SQLConnection.type.html#rollback(io.vertx.core.Handler)[rollback]`.

Once the commit/rollback is complete the handler will be called and the next transaction will be automatically started.

[source,java]
----

// Do stuff with connection - updates etc

// Now commit

connection.commit((Throwable? res) {
  if (!exists res) {
    // Committed OK!
  } else {
    // Failed!
  };
});


----

=== Closing connections

When you've done with the connection you should return it to the pool with `link:../../ceylondoc/vertx-sql//SQLConnection.type.html#close(io.vertx.core.Handler)[close]`.