大约有 11,400 项符合查询结果（耗时：0.0337秒） [XML]
mongodb: insert if not exists
...
Sounds like you want to do an "upsert". MongoDB has built-in support for this. Pass an extra parameter to your update() call: {upsert:true}. For example:
key = {'key':'value'}
data = {'key2':'value2', 'key3':'value3'};
coll.update(key, data, upsert=True); #In python ...
How to create a generic array in Java?
...that mean?
Checked: strong typing. GenSet knows explicitly what type of objects it contains (i.e. its constructor was explicitly called with a Class<E> argument, and methods will throw an exception when they are passed arguments that are not of type E. See Collections.checkedCollection.
-&g...
Retrieving the last record in each group - MySQL
There is a table messages that contains data as shown below:
27 Answers
27
...
explicit casting from super class to subclass
...ssignment Dog dog = (Dog) animal; does not generate a compilation error, but at runtime it generates a ClassCastException . Why can't the compiler detect this error?
...
What Vim command(s) can be used to quote/unquote words?
...te/unquote words and change quoting (e.g. from ' to " ) in Vim? I know about the surround.vim plugin, but I would like to use just Vim.
...
How to access outer class from an inner class?
...
The methods of a nested class cannot directly access the instance attributes of the outer class.
Note that it is not necessarily the case that an instance of the outer class exists even when you have created an instance of the inner class.
In fact, it is often recommended against using nested...
Are strongly-typed functions as parameters possible in TypeScript?
...he types of its argument and its return type. Here we specify that the callback parameter's type must be "function that accepts a number and returns type any":
class Foo {
save(callback: (n: number) => any) : void {
callback(42);
}
}
var foo = new Foo();
var strCallback = (resul...
Remove rows with duplicate indices (Pandas DataFrame and TimeSeries)
I'm reading some automated weather data from the web. The observations occur every 5 minutes and are compiled into monthly files for each weather station. Once I'm done parsing a file, the DataFrame looks something like this:
...
Creating an R dataframe row-by-row
I would like to construct a dataframe row-by-row in R. I've done some searching, and all I came up with is the suggestion to create an empty list, keep a list index scalar, then each time add to the list a single-row dataframe and advance the list index by one. Finally, do.call(rbind,) on the list...
What's the difference between Git Revert, Checkout and Reset?
I am trying to learn how to restore or rollback files and projects to a prior state, and don't understand the difference between git revert , checkout , and reset . Why are there 3 different commands for seemingly the same purpose, and when should someone choose one over the other?
...