Printing the results from a select query with Genie - sqlite

Question

I have created the database in SQL lite and improved the little program to handle it (list, add, remove records). At this point I am trying to list the contents from the database using the prepared statement step() function. However, I can't iterate over the rows and columns on the database.
I suspect that the reason for that is that I am not handling the statement appropriately in this line:
stmt:Sqlite.Statement = null
If that is the case, how to pass the statement from the main (init) function to the children function?
This is the entire code so far:
// Trying to do a cookbook program
// raw_imput for Genie included, compile with valac --pkg sqlite3 cookbook.gs
[indent=4]
uses Sqlite
def raw_input (query:string = ""):string
stdout.printf ("%s", query)
return stdin.read_line ()
init
db : Sqlite.Database? = null
if (Sqlite.Database.open ("cookbook.db3", out db) != Sqlite.OK)
stderr.printf ("Error: %d: %s \n", db.errcode (), db.errmsg ())
Process.exit (-1)
loop:bool = true
while loop = true
print "==================================================="
print " RECIPE DATABASE "
print " 1 - Show All Recipes"
print " 2 - Search for a recipe"
print " 3 - Show a Recipe"
print " 4 - Delete a recipe"
print " 5 - Add a recipe"
print " 6 - Print a recipe"
print " 0 - Exit"
print "==================================================="
response:string = raw_input("Enter a selection -> ")
if response == "1" // Show All Recipes
PrintAllRecipes()
else if response is "2" // Search for a recipe
pass
else if response is "3" //Show a Recipe
pass
else if response is "4"//Delete a recipe
pass
else if response is "5" //Add a recipe
pass
else if response is "6" //Print a recipe
pass
else if response is "0" //Exit
print "Goodbye"
Process.exit (-1)
else
print "Unrecognized command. Try again."
def PrintAllRecipes ()
print "%-5s%-30s%-20s%-30s", "Item", "Name", "Serves", "Source"
print "--------------------------------------------------------------------------------------"
stmt:Sqlite.Statement = null
param_position:int = stmt.bind_parameter_index ("$UID")
//assert (param_position > 0)
stmt.bind_int (param_position, 1)
cols:int = stmt.column_count ()
while stmt.step () == Sqlite.ROW
for i:int = 0 to cols
i++
col_name:string = stmt.column_name (i)
val:string = stmt.column_text (i)
type_id:int = stmt.column_type (i)
stdout.printf ("column: %s\n", col_name)
stdout.printf ("value: %s\n", val)
stdout.printf ("type: %d\n", type_id)
/* while stmt.step () == Sqlite.ROW
col_item:string = stmt.column_name (1)
col_name:string = stmt.column_name (2)
col_serves:string = stmt.column_name (3)
col_source:string = stmt.column_name (4)
print "%-5s%-30s%-20s%-30s", col_item, col_name, col_serves, col_source */
Extra questions are:
Does the definitions of functions should come before or after init? I have noticed that they wouldn't be called if I left all of them after init. But by leaving raw_input in the beginning the error disappeared.
I was trying to define PrintAllRecipes() within a class, for didactic reasons. But I ended up making it "invisible" to the main routine.
Many thanks,

Answer 1

Yes, you need to assign a prepared statement, not null, to stmt. For example:
// Trying to do a cookbook program
// raw_input for Genie included, compile with
// valac --pkg sqlite3 --pkg gee-0.8 cookbook.gs
[indent=4]
uses Sqlite
init
db:Database
if (Database.open ("cookbook.db3", out db) != OK)
stderr.printf ("Error: %d: %s \n", db.errcode (), db.errmsg ())
Process.exit (-1)
while true
response:string = UserInterface.get_input_from_menu()
if response is "1" // Show All Recipes
PrintAllRecipes( db )
else if response is "2" // Search for a recipe
pass
else if response is "3" //Show a Recipe
pass
else if response is "4"//Delete a recipe
pass
else if response is "5" //Add a recipe
pass
else if response is "6" //Print a recipe
pass
else if response is "0" //Exit
print "Goodbye"
break
else
print "Unrecognized command. Try again."
namespace UserInterface
def get_input_from_menu():string
show_menu()
return raw_input("Enter a selection -> ")
def raw_input (query:string = ""):string
stdout.printf ("%s", query)
return stdin.read_line ()
def show_menu()
print """===================================================
RECIPE DATABASE
1 - Show All Recipes
2 - Search for a recipe
3 - Show a Recipe
4 - Delete a recipe
5 - Add a recipe
6 - Print a recipe
0 - Exit
==================================================="""
namespace PreparedStatements
def select_all( db:Database ):Statement
statement:Statement
db.prepare_v2( """
select name, servings as serves, source from Recipes
""", -1, out statement )
return statement
def PrintAllRecipes ( db:Database )
print "%-5s%-30s%-20s%-30s", "Item", "Name", "Serves", "Source"
print "--------------------------------------------------------------------------------------"
stmt:Statement = PreparedStatements.select_all( db )
cols:int = stmt.column_count ()
var row = new dict of string, string
item:int = 1
while stmt.step() == ROW
for i:int = 0 to (cols - 1)
row[ stmt.column_name( i ) ] = stmt.column_text( i )
stdout.printf( "%-5s", item.to_string( "%03i" ))
stdout.printf( "%-30s", row[ "name" ])
stdout.printf( "%-20s", row[ "serves" ])
stdout.printf( "%-30s\n", row[ "source" ])
item++
A few pointers
Generally you want to avoid assigning null. null is no value. For example a boolean can either be true or false and nothing else, but a variable that can have no value makes things more complicated.
a:bool? = null
if a == null
print "I'm a boolean variable, but I am neither true nor false???"
If you are looking to declare a variable in Genie before assigning a value, for example when calling a function with an out parameter, don't assign anything. I have changed db:Database to show this
Process.exit( -1 ) should probably be used sparingly and really only for error conditions that you want to signal to a calling command line script. I don't think a user selected exit from the program is such an error condition, so I have changed Process.exit( -1 ) to break for that
The definition of functions doesn't matter whether it is before or after init, I prefer to put them after so the first function that is called, i.e. init, is at the top and easy to read
A class is a data type and yes, it can have functions, but usually you need some data defined in the class and the function is written to act on that data. A function in a class is often called a 'method' and in the past with object oriented programming classes were defined to group methods together. These methods had no data to act on and are defined as 'static' methods. The modern practise is to mainly use static methods for creating more complex object constructors, look up 'factory' methods and creational design patterns. Instead to group functions, and other syntax, we use namespaces. I have used a couple of namespaces in the example. Usually a namespace is given its own file or files. If you are thinking of splitting your Genie project into more source files then take a look at https://wiki.gnome.org/Projects/Genie#A_Simple_Build_Script
A primary key should be internal to the database and would not be presented to a user, only a database administrator would be interested in such things. So I have changed 'item' in the output to be a count of the number of entries displayed
Genie and Vala bind the SQLite C interface. If you need more details on a particular function take a look at C-language Interface Specification for SQLite