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How do you query for “is not null” in Mongo?
...rue}});
This will return all documents with both a key called "IMAGE URL" and a non-null value.
db.mycollection.find({"IMAGE URL":{$ne:null}});
Also, according to the docs, $exists currently can't use an index, but $ne can.
Edit: Adding some examples due to interest in this answer
Given these inse...
Can I pass parameters by reference in Java?
...itself which is passed by value, hence it appears to be pass-by-reference (and people often claim that it is). This is not the case, as shown by the following:
Object o = "Hello";
mutate(o)
System.out.println(o);
private void mutate(Object o) { o = "Goodbye"; } //NOT THE SAME o!
Will print Hello...
Message 'src refspec master does not match any' when pushing commits in Git
... Don't just follow this step blindly, look at what @Vi has mentioned, and then modify your push command to correct ref.
– Kumar
Jun 7 '12 at 16:43
54
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Read file from line 2 or skip header row
How can I skip the header row and start reading a file from line2?
8 Answers
8
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com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
...tions.
DB server has run out of connections.
Something in between Java and DB is blocking connections, e.g. a firewall or proxy.
To solve the one or the other, follow the following advices:
Verify and test them with ping.
Refresh DNS or use IP address in JDBC URL instead.
...
How to avoid “RuntimeError: dictionary changed size during iteration” error?
...n you want to delete an object in inner dict. for example you have a dic A and dict B in dict A. if you want to delete object in dict B it occurs error
– Ali-T
Apr 18 at 6:35
1
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What is the purpose of std::make_pair vs the constructor of std::pair?
...hink you can do one = {10, 20} nowadays but I don't have a C++11 compiler handy to check it.
– MSalters
Feb 14 '12 at 8:11
6
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Cython: “fatal error: numpy/arrayobject.h: No such file or directory”
... You don't need to create a setup.py ... you don't need to even open a command line if you use IPython ... it's all very convenient. In your case, try running these commands in IPython or in a normal Python script:
import numpy
import pyximport
pyximport.install(setup_args={"script_args":["--compil...
Why do I get an UnsupportedOperationException when trying to remove an element from a List?
...|")
On better algorithm
Instead of calling remove one at a time with random indices, it's better to generate enough random numbers in the range, and then traversing the List once with a listIterator(), calling remove() at appropriate indices. There are questions on stackoverflow on how to gener...
How can I change the thickness of my tag
...
For consistency remove any borders and use the height for the <hr> thickness. Adding a background color will style your <hr> with the height and color specified.
In your stylesheet:
hr {
border: none;
height: 1px;
/* Set the hr color ...