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What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
The "N+1 selects problem" is generally stated as a problem in Object-Relational mapping (ORM) discussions, and I understand that it has something to do with having to make a lot of database queries for something that seems simple in the object world.
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Correct way to use get_or_create?
...f the fields have to be included in defaults. In case CREATE event occurs, all the fields are taken into consideration.
It looks like you need to be returning into a tuple, instead of a single variable, do like this:
customer.source,created = Source.objects.get_or_create(name="Website")
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is not JSON serializable
...fe tage. stackoverflow.com/a/57939897/4157431
– Rami Alloush
Sep 14 '19 at 23:01
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How do I cast a variable in Scala?
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The preferred technique is to use pattern matching. This allows you to gracefully handle the case that the value in question is not of the given type:
g match {
case g2: Graphics2D => g2
case _ => throw new ClassCastException
}
This block replicates the semantics of th...
Can the jQuery UI Datepicker be made to disable Saturdays and Sundays (and holidays)?
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There is the beforeShowDay option, which takes a function to be called for each date, returning true if the date is allowed or false if it is not. From the docs:
beforeShowDay
The function takes a date as a parameter and must return an array with [0] equal to true/false indicating wh...
get path for my .exe [duplicate]
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in visualstudio 2008 you could use this code :
var _assembly = System.Reflection.Assembly
.GetExecutingAssembly().GetName().CodeBase;
var _path = System.IO.Path.GetDirectoryName(_assembly) ;
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how to clear the screen in python [duplicate]
... To avoid the 0 (system's return value) being shown, use absolutely_unused_variable = os.system("cls") or absolutely_unused_variable = os.system("clear")
– Shiva
Jul 4 '15 at 8:01
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Installed Ruby 1.9.3 with RVM but command line doesn't show ruby -v
... what do you do if env has a lot of rvm stuff in it still? like rvm_dump_environment_flag=0 etc...
– jcollum
Apr 22 '12 at 21:28
5
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Apache not starting on MAMP Pro
.... Go to bin -> apache2 -> bin.
Then rename the file from envvars to _envvars.
I also came across another problem of it not working correctly. Make sure the ports are Apache defaults, NOT MAMP defaults (port 80 etc). If it works straight away, this should not apply to you.
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CMap用法 - C/C++ - 清泛网 - 专注C/C++及内核技术
...的效率。CMap就是对Hash表的一种实现。先上实例：
int _tmain(int argc, char* argv[])
{
//定义
typedef CMap<int, int, CString, CString> CMapInt;
CMapInt map;
//添加key，val
map.SetAt(1, "str1");
map.SetAt(2, "str2");
map.SetAt(3, "str3");
map.SetAt(1, "s...