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DanteX
Apprentice
Joined: 13 Aug 2007
Posts: 166
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 Posted: Sat Dec 05, 2009 9:04 am
[3.12] Endless loop when using #WHILE (!@row.Eof()) and calling an SQLite db
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I have a database with 2 records, for testing.
| Code: |
#VAR row %sql(@DB_name, "SELECT * FROM MobList")
#LOOP 5 {
#SHOW "MobName: " @row.Item("MobName"), Position: @row.Position
#CALL @row.Next
}
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displays:
MobName: A Living Rock, Position: 1
MobName: Some Reeds, Position: 2
MobName: Some Reeds, Position: 2
MobName: Some Reeds, Position: 2
MobName: Some Reeds, Position: 2
But the following code gets stuck in an endless loop:
| Code: |
#VAR row %sql(@DB_name, "SELECT * FROM MobList")
#WHILE (!@row.Eof()) {
#SHOW "MobName: " @row.Item("MobName"), Position: @row.Position
#CALL @row.Next
}
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It's like the .Eof() flag won't work. The same endless loop occurs when I use this alias below and search for "Some Reeds" e.g.
| Code: |
#IF (%0) {
#VAR db_search_string %0
#VAR row %sql( @DB_name, "SELECT * FROM MobList WHERE MobName LIKE" '@db_search_string')
#MXP %ansi( Red, high)Results for mob: %ansi( White, high)'@db_search_string'
#WHILE (!@row.Eof()) {
#SHOW "MobName: " @row.Item("MobName"), Position: @row.Position
#CALL @row.Next
}
}
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The resulting output from that operation is, and I have to hit ESC to abort the loop:
Results for mob: 'Some Reeds'
MobName: Some Reeds, Position: 1
MobName: Some Reeds, Position: 1
MobName: Some Reeds, Position: 1
MobName: Some Reeds, Position: 1
MobName: Some Reeds, Position: 1
When I use the muds.db file to test, I use the following code, and the result is displayed below the code (only the end of the spam).
| Code: |
#VAR row %sql(muds, "SELECT * FROM MudList")
#WHILE (!@row.Eof()) {
#SHOW "Title: " @row.Item("Title")
#CALL @row.Next
}
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Title: DragonBall A New Dimension
Title: Reality Dysfunction
Title: Creeping Death II
Title: Realms of Talos
Title: Cory Mud
Title: Celestial Knights
Title: Asgardian Nightmare: Chaos Theory
Title: Asgardian Nightmare: Chaos Theory
Title: Asgardian Nightmare: Chaos Theory
Title: Asgardian Nightmare: Chaos Theory
Title: Asgardian Nightmare: Chaos Theory
Title: Asgardian Nightmare: Chaos Theory
(ESC had to be hit to stop the loop)
Bug in .Eof?
//DanteX |
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Zugg
MASTER
Joined: 25 Sep 2000
Posts: 23379
Location: Colorado, USA
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Posted: Mon Dec 07, 2009 9:21 pm
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Confirmed and added to bug list. The EOF function is part of the SQLite driver, so I have no idea why it's not returning the correct value, but I'll look into it. It certainly needs to be fixed to make looping through databases useful. And I don't remember seeing any problem like this in zApp. Maybe it's an SQLite v3 issue? (zApp only used SQLite v2)
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Zugg
MASTER
Joined: 25 Sep 2000
Posts: 23379
Location: Colorado, USA
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Posted: Wed Jan 27, 2010 10:53 pm
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Well, I found this bug, and it's really an annoying and stupid one.
The "@row.Next" method actually calls the ZeosLib "MoveNext" method, which supports moving through a filtered dataset rather than just the raw records. And while MoveNext returns true or false depending upon it it's successful, it does NOT set the EOF flag at the end. Grrr...
I guess they thought that since EOF means "End of File" and with a filtered dataset you are just at the last record in the filter and not necessarily at the last record in the entire database file.
The problem with this is that the Delphi EOF method for generic DataSet objects is a READONLY property. So I have no way to set this property myself when MoveNext returns false. Looks like I need to completely override the Delphi EOF property with my own and then handle this all myself. What a pain. |
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chris-74269
Magician
Joined: 23 Nov 2004
Posts: 364
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Posted: Wed Jan 27, 2010 11:56 pm
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For the time being, you could check the record index with %item(@row.List,1) and if it matches the previous one, stop there.
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Rahab
Wizard
Joined: 22 Mar 2007
Posts: 2320
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Posted: Thu Jan 28, 2010 2:55 pm
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Does @row.Next return a TRUE/FALSE value? If so, testing for a FALSE would be another workaround.
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Zugg
MASTER
Joined: 25 Sep 2000
Posts: 23379
Location: Colorado, USA
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Posted: Thu Jan 28, 2010 5:20 pm
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Yes, @row.Next returns false when you get to the end of the database, but I still wanted to fix @row.Eof also. I got this all fixed yesterday for the next version, so it's no longer an issue.
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