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What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
...s (also rows). In other words, Car → Wheel is a 1-to-many relationship.
Now, let's say you need to iterate through all the cars, and for each one, print out a list of the wheels. The naive O/R implementation would do the following:
SELECT * FROM Cars;
And then for each Car:
SELECT * FROM Wheel W...
R memory management / cannot allocate vector of size n Mb
...to a minimum when you need to make objects of this size. Use gc() to clear now unused memory, or, better only create the object you need in one session.
If the above cannot help, get a 64-bit machine with as much RAM as you can afford, and install 64-bit R.
If you cannot do that there are many o...
How to build a jar using maven, ignoring test results? [duplicate]
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Anyone know why "-Dmaven.test.error.ignore=true" is not being used anymore? I finding the need to not ignore actual failures, but ignore errors (which may not actually cause the test to "fail") in some cases. Is there any way to di...
Eclipse error: 'Failed to create the Java Virtual Machine'
... any other text-editor application, Find the line -Xmx256m (or -Xmx1024m). Now change the default value 256m (or 1024m) to 512m. You also need to give the exact java installed version (1.6 or 1.7 or other).
Like This:
-Xmx512m
-Dosgi.requiredJavaVersion=1.6
OR
-Xmx512m
-Dosgi.requiredJavaVers...
Mimicking sets in JavaScript?
...or somethings called ES 2015 has a built-in Set object. It is implemented now in some browsers. Since browser availability changes over time, you can look at the line for Set in this ES6 compatibility table to see the current status for browser availability.
One advantage of the built-in Set objec...
How to check command line parameter in “.bat” file?
...n do an if/else switch on -b: if "%~1"=="-b" (goto specific) else goto unknown
Surrounding the parameters with quotes makes checking for things like blank/empty/missing parameters easier. "~" ensures double quotes are stripped if they were on the command line argument.
...
Add a reference column migration in Rails 4
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Now, if you use the special generator syntax for migrations, Rails 4.2 will automatically create the correct migration with foreign key constraints included. rails g migration AddUserToUploads user:references produces add_ref...
Generic deep diff between two objects
...d to format diff object in arbitrary way based on passed primitive values (now this job is done by "compareValues" method).
var deepDiffMapper = function () {
return {
VALUE_CREATED: 'created',
VALUE_UPDATED: 'updated',
VALUE_DELETED: 'deleted',
VALUE_UNCHANGED: 'unchanged',
...
What is the list of possible values for navigator.platform as of today? [closed]
I know that this changes quite often, but is there a list as exhaustive as possible out there of the possible values returned by navigator.platform ?
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Why must a lambda expression be cast when supplied as a plain Delegate parameter
...her be converted to a delegate type or an expression tree - but it has to know which delegate type. Just knowing the signature isn't enough. For instance, suppose I have:
public delegate void Action1();
public delegate void Action2();
...
Delegate x = () => Console.WriteLine("hi");
What woul...