大约有 44,000 项符合查询结果（耗时：0.0493秒） [XML]
PostgreSQL Autoincrement
I'm switching from MySQL to PostgreSQL and was wondering how I can do autoincrement values. I saw in the PostgreSQL docs a datatype "serial", but I get syntax errors when using it (in v8.0).
...
How to map and remove nil values in Ruby
...
Ruby 2.7 is introducing filter_map for this exact purpose. It's idiomatic and performant, and I'd expect it to become the norm very soon.
For example:
numbers = [1, 2, 5, 8, 10, 13]
enum.filter_map { |i| i * 2 if i.even? }
# => [4, 16, 20]
In your case, as the block evaluates to falsey, simp...
What are the differences between Perl, Python, AWK and sed? [closed]
just want to know what are the main differences among them? and the power of each language (where it's better to use it).
5...
Django: “projects” vs “apps”
... ready to build using Django. I'm going to avoid using the terms "project" and "application" in this context, because I'm not clear on their specific meaning in Django.
...
Android ViewPager - Show preview of page on left and right
I'm using Android's ViewPager . What I want to do is to show a preview of the page on both the left and the right. I've seen where I can use a negative pageMargin to show a preview of the right side.
...
Create unique constraint with null columns
...(user_id, menu_id, recipe_id), you cannot base CLUSTER on a partial index, and queries without a matching WHERE condition cannot use the partial index. (It seems unlikely you'd want a FK reference three columns wide - use the PK column instead).
If you need a complete index, you can alternatively d...
When to use symbols instead of strings in Ruby?
...ommon because many programming languages don't have symbols, only strings, and thus strings are also used as identifiers in your code. You should be worrying about what symbols are meant to be, not only when you should use symbols. Symbols are meant to be identifiers. If you follow this philosophy, ...
Automapper - how to map to constructor parameters instead of property setters
...
Looks like CreateMap<> should be PersonViewModel and not PersonProfile. As well as in the second code block PersonModel should be PersonViewModel.
– Ben Sampica
Aug 7 '19 at 19:30
...
How do you rename a MongoDB database?
There's a typo in my MongoDB database name and I'm looking to rename the database.
10 Answers
...
Factory pattern in C#: How to ensure an object instance can only be created by a factory class?
... method of a factory class. Let us say I have some "business object" class and I want to make sure any instance of this class will have a valid internal state. In order to achieve this I will need to perform some check before creating an object, probably in its constructor. This is all okay until I ...