Classes reading and writing to the data heap would communicate directly
with the Heap object, and transfer ByteBuffers back and forth with it.
This makes things like caching and locking hard. Therefore all data
persistence activity will be funneled through a Serializer object which
in turn submits it to the Heap.
Introducing this unfortunately resulted in a huge amount of churn, in
which a number of smaller refactorings got caught up as well.
This patch provides very basic, bare bones implementations of the
INSERT and SELECT statements. They are *very* limited:
- The only variant of the INSERT statement that currently works is
SELECT INTO schema.table (column1, column2, ....) VALUES
(value11, value21, ...), (value12, value22, ...), ...
where the values are literals.
- The SELECT statement is even more limited, and is only provided to
allow verification of the INSERT statement. The only form implemented
is: SELECT * FROM schema.table
These statements required a bit of change in the Statement::execute
API. Originally execute only received a Database object as parameter.
This is not enough; we now pass an ExecutionContext object which
contains the Database, the current result set, and the last Tuple read
from the database. This object will undoubtedly evolve over time.
This API change dragged SQLServer::SQLStatement into the patch.
Another API addition is Expression::evaluate. This method is,
unsurprisingly, used to evaluate expressions, like the values in the
INSERT statement.
Finally, a new test file is added: TestSqlStatementExecution, which
tests the currently implemented statements. As the number and flavour of
implemented statements grows, this test file will probably have to be
restructured.
This patch introduces the ability execute parsed SQL statements. The
abstract AST Statement node now has a virtual 'execute' method. This
method takes a Database object as parameter and returns a SQLResult
object.
Also introduced here is the CREATE SCHEMA statement. Tables live in a
schema, and if no schema is present in a table reference the 'default'
schema is implied. This schema is created if it doesn't yet exist when
a Database object is created.
Finally, as a proof of concept, the CREATE SCHEMA and CREATE TABLE
statements received an 'execute' implementation. The CREATE TABLE
method is not able to create tables created from SQL queries yet.