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MongoDB数据导出导入工具：mongoexport,mongoimport - 大数据 & AI - 清泛...
...t. default: json (json,csv,tsv)
--file arg file to import from; if not specified stdin is used
--drop drop collection first
--headerline CSV,TSV only - use first line as headers
--upsert insert or update objects that already exist
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What does ||= (or-equals) mean in Ruby?
...ake ||= behave more like the second expansion. (I based this on an example from one of the threads linked to in another answer.)
– antinome
Oct 10 '14 at 16:08
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In Scala, what exactly does 'val a: A = _' (underscore) mean?
...huck says in his answer, this initialises the variable to a default value. From the Scala Language Specification:
0 if T is Int or one of its subrange types,
0L if T is Long,
0.0f if T is Float,
0.0d if T is Double,
false if T is Boolean,
() if T is Unit,
null for all other types T.
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What is the difference between window, screen, and document in Javascript?
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The comment from @Mandy confuses window with viewport. A window is the JavaScript object for the browser tab or <iframe> (or deprecated <frame>). The viewport is the rectangle of the rendered document seen within the tab or f...
Why should I use document based database instead of relational database?
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CouchDB (from their website)
A document database server, accessible via a RESTful JSON API. Generally, relational databases aren't simply accessed via REST services, but require a much more complex SQL API. Often these API's (JDB...
Modulus % in Django template
...t row even if there are less than 4 items.
myapp/templatetags/my_tags.py
from django import template
register = template.Library()
@register.filter
def modulo(num, val):
return num % val
html template
{% load my_tags %}
{% for item in all_items %}
{% if forloop.counter|modulo:4 == 1...
Excel: last character/string match in a string
...of "@", I used CHAR(9) (the tab character), since my data originally comes from tab-delimited file, and I'm guaranteed it won't be in my data.
– Josiah Yoder
Jun 16 '15 at 21:11
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Meaning
...dition has no effect and all managed modules run for all requests.
Copied from IIS Modules Overview: Preconditions
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Make a URL-encoded POST request using `http.NewRequest(…)`
...wReader(s string) *Reader, it says "NewReader returns a new Reader reading from s. It is similar to bytes.NewBufferString but more efficient and read-only."
– Liyang Chen
Apr 12 '16 at 5:23
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Difference between Key, Primary Key, Unique Key and Index in MySQL
...d someone by the last name: We don't start searching through the directory from cover to cover, as long we inserted the information in some order that we can use to skip quickly to the 'S' pages.
Primary keys and unique keys are similar. A primary key is a column, or a combination of columns, that ...