[Tarantool-discussions] RFC - distributed SQL, step #1 - AST

[Nikita Pettik]

On 25 Nov 01:06, Timur Safin wrote:
> 
> Exporting AST as cdata is easy to do, but in this case it will be 
> inconvenient to manipulate AST nodes, before sending to cluster nodes.
> So there is 2nd, more idiomatic approach suggested - to convert AST
> to nested Lua object/tables.

Hm, why do you need those tables? Serialization into msgpack can
be done inside SQL internals.

> Which should simplify some massaging
> and provide natural way to serialization to msgpack.
> 
> 
> SYNOPSIS
> ~~~~~~~~
> 
> .. code-block:: lua
> 
>    local sql = require `sqlparser`
> 
>    -- parse, return ast, pass it back unmodified for execution
> 
>    local ast = sql.parse [[ select * from "table" where id > 10 limit 10 ]]

Should this be public API? Alternatively, we can hide it in sql.internals.

>    assert(type(ast) == 'cdata')
>    local ok = sql.execute(ast)
> 
>    -- free allocated memory, like box.unprepare but for ast
>    sql.unparse(ast)

I don't like unparse name. In fact even unprepare is a bad name,
it should be called sort of deallocate. I suggest sql.release_ast()/
sql.free_ast() naming.
 
>    -- raw access to cdata structures
>    local cdata = ast.as_cdata()
>    if cdata.ast_type == ffi.C.AST_TYPE_SELECT
>       handle_select_stmt(cdata.select)
>    end
> 
>    -- Lua access to structurs as Lua tables
>    local tree = ast.as_table()
>    if tree.type == AST_TYPE_SELECT
>       handle_columns_list(tree.select.columns)
>       handle_where_clause(tree.select.where)
>       limit = tree.select.limit

What's the purpose of these handles?

>    end
>    -- massaging with tree data
> 
>    -- serialization
>    local msgpack = require 'msgpack'
>    local to_wire = msgpack.encode(tree)
> 
>    -- networking magics ...
>    -- ... deserialization
>    local table = msgpack.decode(from_wire)
>    ast.set_tree(tree)
>    sql.execute(ast)
> 
> 
> Regards,
> Timur
> 
> P.S.
>