keys

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: Rails has no way of creating foreign keys in migrations (there are plugins to do this, however). There are also plenty of cascading options so you can get cascading deletes, for example. With all of these options built in, is it worth creating foreign keys in the database? Is this something Rails developers normally avoid or what? You'd think if it was a recommended practice that Rails would natively support it. 回答1: This is something of a holy issue, because DHH (the creator of Rails) has stated before that he sees the database as

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I have searched for key value stores that support integer keys and integer values. LevelDB seems a good option, though I can't find any information on whether integer values/keys are supported 回答1: You can store pretty much anything in LevelDB. You provide opaque slices of data into LevelDB via the Slice structure. Here is an example: int intKey = 256; int intValue = 256*256; Slice key((char*)&intKey, sizeof(int)); Slice value((char*)&intValue, sizeof(int)); db->Put(leveldb::WriteOptions(), key, value); And that's pretty much it! However ,

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I have a MIFARE 1K tag. Some blocks can be written/read using authentication key A, while other block can be written using authentication key B. Why? How can I change all blocks to be written/read, for example, with key A? For example, I can write the key block 07 using key A, and I can also change the key A for this key block, but I can't write on it using key B, and I can't change the key B for this key block. Why should I write/read using key A instead of key B? What's the difference? 回答1: Each sector of a MIFARE Classic card has two

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I have a couple of NSString objects that represent an RSA public-private keypair (not generated by SecKeyCreatePair, but by an external crypto library). How can I create SecKeyRef objects (which are required for the SecKeyDecrypt/Encrypt methods) from these NSString objects? Do I need to import them into the Keychain first? If so, how? Thanks! 回答1: So in iOS, the keychain is sandboxed, AFAIK. This means that whatever you put into the keychain is only accessible by your app and your app alone unless you specify otherwise. You have to enable

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: The book Numerical Recipes offers a method to calculate 64bit hash codes in order to reduce the number of collisions. The algorithm is shown at http://www.javamex.com/tutorials/collections/strong_hash_code_implementation_2.shtml and is copied here for reference: private static final createLookupTable() { byteTable = new long[256]; long h = 0x544B2FBACAAF1684L; for (int i = 0; i < 256; i++) { for (int j = 0; j < 31; j++) { h = (h >>> 7) ^ h; h = (h << 11) ^ h; h = (h >>> 10) ^ h; } byteTable[i] = h; } return byteTable; } public static long

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I'm using Hibernate with annotations (in spring), and I have an object which has an ordered, many-to-one relationship which a child object which has a composite primary key, one component of which is a foreign key back to the id of the parent object. The structure looks something like this: +=============+ +================+ | ParentObj | | ObjectChild | +-------------+ 1 0..* +----------------+ | id (pk) |-----------------| parentId | | ... | | name | +=============+ | pos | | ... | +================+ I've tried a variety of combinations of

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 由 翻译 强力驱动 问题: I've been trying to display a Generic Foreign Key in the Django admin but can't get it working. I have a FullCitation class that can be linked to either a NonSupportedProgram or a SupportedProgram class. So, I have used a generic foreign key. In the admin, I want users to only be able to select 'NonSupportedProgram' or 'SupportedProgram' from the content_type dropdown and then, from the object_id field, I need users to be able to select from a dropdown listing the existing NonSuportedPrograms or the existing Supported Programs,

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 由 翻译 强力驱动 问题: I've been trying to display a Generic Foreign Key in the Django admin but can't get it working. I have a FullCitation class that can be linked to either a NonSupportedProgram or a SupportedProgram class. So, I have used a generic foreign key. In the admin, I want users to only be able to select 'NonSupportedProgram' or 'SupportedProgram' from the content_type dropdown and then, from the object_id field, I need users to be able to select from a dropdown listing the existing NonSuportedPrograms or the existing Supported Programs,

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: Does anybody know if there is a built-in function in Mathematica for getting the lhs of downvalue rules (without any holding)? I know how to write the code to do it, but it seems basic enough for a built-in For example: a[1]=2; a[2]=3; BuiltInIDoNotKnowOf[a] returns {1,2} 回答1: This seems to work; not sure how useful it is, though: a[1] = 2 a[2] = 3 a[3] = 5 a[6] = 8 Part[DownValues[a], All, 1, 1, 1] 回答2: This is like keys() in Perl and Python and other languages that have built in support for hashes (aka dictionaries). As your example

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I need to create a very long string in a program, and have been using String.Format. The problem I am facing is keeping track of all the numbers when you have more than 8-10 parameters. Is it possible to create some form of overload that will accept a syntax similar to this? String.Format("You are {age} years old and your last name is {name} ", {age = "18", name = "Foo"}); 回答1: How about the following, which works both for anonymous types (the example below), or regular types (domain entities, etc): static void Main() { string s = Format(