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digitalmars.D.learn - Question about mysql-d Object

reply Martin Tschierschke <mt smartdolphin.de> writes:
When I do the following:

auto mysql = new Mysql("localhost", 3306, "mt", "", "verwaltung");
auto rows = mysql.query("select field from my_table limit 50");

foreach(row;rows){
  writeln(row["field"]);}

// second time same loop

foreach(row;rows){
  writeln(row["field"]);}

I only get the output of the first loop (50 lines), probably this 
is a feature
not a bug, but what kind of Object is rows?

A nested loop, did not worked either:

foreach(row;rows){
  foreach(field;row){
  writeln(field);}
}

Which other ways to access the elements of rows do I have?

Sorry, but I am very new on D, (it may be the best language 
available, I don't know yet, but it is really the most 
interesting!) thank you!
Dec 07 2015
next sibling parent =?UTF-8?B?TcOhcmNpbw==?= Martins <marcioapm gmail.com> writes:
On Monday, 7 December 2015 at 14:40:12 UTC, Martin Tschierschke 
wrote:

 When I do the following:

 auto mysql = new Mysql("localhost", 3306, "mt", "", 
 "verwaltung");
 auto rows = mysql.query("select field from my_table limit 50");

 foreach(row;rows){
  writeln(row["field"]);}

 // second time same loop

 foreach(row;rows){
  writeln(row["field"]);}

 I only get the output of the first loop (50 lines), probably 
 this is a feature
 not a bug, but what kind of Object is rows?

 A nested loop, did not worked either:

 foreach(row;rows){
  foreach(field;row){
  writeln(field);}
 }

 Which other ways to access the elements of rows do I have?

 Sorry, but I am very new on D, (it may be the best language 
 available, I don't know yet, but it is really the most 
 interesting!) thank you!


I suppose that's because the rows object is a mysql cursor, which 
means you can only iterate it once, and only forward (Not sure 
how it is implemented in mysql-d). It seems like your inner loop 
is exhausting it.

If you need random access or multiple iterations, you first need 
to copy your rows into another array/structure, and then you can 
do whatever you want with it.
Dec 07 2015
prev sibling parent reply Daniel Kozak <kozzi11 gmail.com> writes:
On Monday, 7 December 2015 at 14:40:12 UTC, Martin Tschierschke 
wrote:

 When I do the following:

 auto mysql = new Mysql("localhost", 3306, "mt", "", 
 "verwaltung");
 auto rows = mysql.query("select field from my_table limit 50");

 foreach(row;rows){
  writeln(row["field"]);}

 // second time same loop

 foreach(row;rows){
  writeln(row["field"]);}

 I only get the output of the first loop (50 lines), probably 
 this is a feature
 not a bug, but what kind of Object is rows?

 A nested loop, did not worked either:

 foreach(row;rows){
  foreach(field;row){
  writeln(field);}
 }

 Which other ways to access the elements of rows do I have?

 Sorry, but I am very new on D, (it may be the best language 
 available, I don't know yet, but it is really the most 
 interesting!) thank you!


what if you make array from it:
import std.array: array;
auto rows = mysql.query("select field from my_table limit 
50").array;
Dec 07 2015
parent reply Martin Tschierschke <mt smartdolphin.de> writes:
On Monday, 7 December 2015 at 16:11:19 UTC, Daniel Kozak wrote:

 On Monday, 7 December 2015 at 14:40:12 UTC, Martin Tschierschke 
 wrote:

 When I do the following:

 auto mysql = new Mysql("localhost", 3306, "mt", "", 
 "verwaltung");
 auto rows = mysql.query("select field from my_table limit 50");

 foreach(row;rows){
  writeln(row["field"]);}

 // second time same loop

 foreach(row;rows){
  writeln(row["field"]);}




[...]

 A nested loop, did not worked either:

 foreach(row;rows){
  foreach(field;row){
  writeln(field);}
 }

 Which other ways to access the elements of rows do I have?




[...]

 what if you make array from it:
 import std.array: array;
 auto rows = mysql.query("select field from my_table limit 
 50").array;


Thank you both for your answers!
This worked, for the first part of my question.
Now I took a work around, getting the field names in a separate 
mysql-request,
but they should be available in the row object, too?
Dec 08 2015
next sibling parent Daniel Kozak via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
V Tue, 08 Dec 2015 14:34:53 +0000
Martin Tschierschke via Digitalmars-d-learn
<digitalmars-d-learn puremagic.com> napsáno:


 On Monday, 7 December 2015 at 16:11:19 UTC, Daniel Kozak wrote:

 On Monday, 7 December 2015 at 14:40:12 UTC, Martin Tschierschke 
 wrote:  

 When I do the following:

 auto mysql = new Mysql("localhost", 3306, "mt", "", 
 "verwaltung");
 auto rows = mysql.query("select field from my_table limit 50");

 foreach(row;rows){
  writeln(row["field"]);}

 // second time same loop

 foreach(row;rows){
  writeln(row["field"]);}
  




 [...]

 A nested loop, did not worked either:

 foreach(row;rows){
  foreach(field;row){
  writeln(field);}
 }

 Which other ways to access the elements of rows do I have?
  




 [...]

 what if you make array from it:
 import std.array: array;
 auto rows = mysql.query("select field from my_table limit 
 50").array;  


 Thank you both for your answers!
 This worked, for the first part of my question.
 Now I took a work around, getting the field names in a separate 
 mysql-request,
 but they should be available in the row object, too?
 


rows.fields();
Dec 08 2015
prev sibling parent reply Daniel Kozak via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
V Tue, 08 Dec 2015 14:34:53 +0000
Martin Tschierschke via Digitalmars-d-learn
<digitalmars-d-learn puremagic.com> napsáno:


 On Monday, 7 December 2015 at 16:11:19 UTC, Daniel Kozak wrote:

 On Monday, 7 December 2015 at 14:40:12 UTC, Martin Tschierschke 
 wrote:  

 When I do the following:

 auto mysql = new Mysql("localhost", 3306, "mt", "", 
 "verwaltung");
 auto rows = mysql.query("select field from my_table limit 50");

 foreach(row;rows){
  writeln(row["field"]);}

 // second time same loop

 foreach(row;rows){
  writeln(row["field"]);}
  




 [...]

 A nested loop, did not worked either:

 foreach(row;rows){
  foreach(field;row){
  writeln(field);}
 }

 Which other ways to access the elements of rows do I have?
  




 [...]

 what if you make array from it:
 import std.array: array;
 auto rows = mysql.query("select field from my_table limit 
 50").array;  


 Thank you both for your answers!
 This worked, for the first part of my question.
 Now I took a work around, getting the field names in a separate 
 mysql-request,
 but they should be available in the row object, too?
 


rows.fieldNames() this one is better result type is string[]
Dec 08 2015
parent Martin Tschierschke <mt smartdolphin.de> writes:
On Tuesday, 8 December 2015 at 15:14:06 UTC, Daniel Kozak wrote:
[...]

 A nested loop, did not worked either:

 foreach(row;rows){
  foreach(field;row){
  writeln(field);}
 }








[...]

 Now I took a work around, getting the field names in a separate
 mysql-request,
 but they should be available in the row object, too?
 


 rows.fieldNames() this one is better result type is string[]


Thank you!!!
Dec 08 2015