我有created the database in SQL lite and improved the little program to handle it（列出，添加，删除记录）。此时，我正在尝试使用预准备语句step（）函数列出数据库中的内容。但是，我无法遍历数据库中的行和列。
我怀疑其原因是我没有在这一行中恰当地处理该陈述：
stmt:Sqlite.Statement = null
如果是这种情况，如何将语句从main（init）函数传递给子函数？
到目前为止，这是完整的代码：
// 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 */
额外的问题是：
函数的定义是应该在init之前还是之后？我注意到如果我在init之后将所有这些都留下，他们就不会被调用。但是通过将raw_input保留在开头，错误就消失了。
出于教学原因，我试图在一个类中定义PrintAllRecipes（）。但我最终把它变成了'＃34;隐形＆＃34;到主程序。
非常感谢，
答案 0 :(得分：1)
是的，您需要为null分配一份准备好的陈述，而不是stmt。例如：
// 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++
一些指示
通常，您希望避免分配null。 null没有价值。例如，布尔值可以是true或false而不是其他任何东西，但是一个没有值的变量会使事情变得更复杂。
a:bool? = null
if a == null
print "I'm a boolean variable, but I am neither true nor false???"
如果您想在分配值之前在Genie中声明变量，例如在调用具有out参数的函数时，请不要分配任何内容。我已更改db:Database以显示此
Process.exit( -1 )应该谨慎使用，实际上只适用于您想要向调用命令行脚本发出信号的错误情况。我不认为用户选择从程序退出是错误的，所以我已将Process.exit( -1 )更改为break init之前还是之后，我更喜欢将它们放在后面，因此调用的第一个函数，即init，位于顶部并且易于阅读