rules | 易学教程

How to use Firebase rules to only give permission to certain leaf nodes

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问题 My basic question is how do you setup Firebase rules to only allow access certain leaf nodes from their parent? Lets say I have data that looks like this: root: { posts: { post1: { user: "foo", post: "this is a post", restricted: false }, post2: { user: "bar", post: "this is another post", restricted: true }, post3: { user: "bar", post: "this is my final post", restricted: false } } } I want to $bind to the posts node and get all the posts which that user is allowed to get. I might want the

Are there any rules for OOP?

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Recently I heard that there are 9 rules for OOP(Java). I know only four as Abstraction, Polymorphism, Inheritance and Encapsulation. Are there any more rules for OOP? Seems like what you're looking for are the Principles of Object-Oriented Design . Summarized from Agile Software Development Principles, Patterns, and Practices . These principles are the hard-won product of decades of experience in software engineering. They are not the product of a single mind, but they represent the integration and writings of a large number of software developers and researchers. Although they are presented

How to validate a JSON object in java?

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问题 I use sf.json library to map form data for incoming request in my web application in java. Lets say the incoming request is http://localhost:8080/app/addProfile with form data as: formData: { "name":"applicant Name", "Age":"26", "academics":{ "college":"80", "inter":"67", "matriculation":"89" }, "skill":{ "computer":"c,c++,java", "maths":"limit,permutation,statistics" }, "dateOfBirth":"09-07-1988" } Server Side : String requestFormData=request.getParameter("formData"); JSONObject formData =

What are PostgreSQL RULEs good for?

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问题 Question I often see it stated that rules should be avoided and triggers used instead. I can see the danger in the rule system, but certainly there are valid uses for rules, right? What are they? I'm asking this out of general interest; I'm not very seasoned with databases. Example of what might be a valid use For instance, in the past I've needed to lock down certain data, so I've done something like this: CREATE OR REPLACE RULE protect_data AS ON UPDATE TO exampletable -- another similar

In ANTLR, is there a shortcut notation for expressing alternation of all the permutations of some set of rules?

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问题 In ANTLR I want to define a rule like this: rule : ( a b c | a c b | b a c | b c a | c a b | c b a ); But in my case I have 10 rules instead of three, that I want to permute so it gets very impractical. Is there any way of expressing this in ANTLR without having to write all the permutations? 回答1: I would just match any a , b or c once or more: rule : ( a | b | c )+ ; and then, after parsing, traversing the parse tree and checking if a , b and c all matched exactly once. But Yes, it is

How can I interpolate a variable into a Perl 6 regex?

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问题 Synopsis 05 mentions that Perl 6 doesn't interpolate variables into a regex, but you can associate an external variable with a pattern. The docs don't mention this feature as far as I can tell. I think people are still going to want to build up a pattern from a string somehow, so I'm curious how that would work. Here's a program that demonstrates what happens now. I don't know if that's what is supposed to happen or what anyone intended. I insert a variable into a pattern. If you look at $r

Device eth0 does not seem to be present,delaying initialization

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centos6.4安装 minimal ifconfig...没有看到eth0.。然后重启网卡又报下面错误。故障现象： service network restart Shutting down loopback insterface: [ OK ] Bringing up loopback insterface: [ OK ] Bringing up interface eth0: Device eth0 does not seem to be present,delaying initialization. [FAILED] 解决办法：首先，打开/etc/udev/rules.d/70-persistent-net.rules内容如下面例子所示： # vi /etc/udev/rules.d/70-persistent-net.rules # This file was automatically generated by the /lib/udev/write_net_rules # program, run by the persistent-net-generator.rules rules file. # # You can modify it, as long as you keep each rule on a single # line, and change

List of C++ name resolution (and overloading) rules

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问题 Where I can find a list of the rules that a C++ compliant compiler must apply in order to perform names resolution (including overloading)? I'd like something like a natural-language algorithm or flow chart. C++ standard of course has this set of rules but it is build up as new language statements are introduced and the result it's pretty hard to remember. To make a long story short, I'd like to know the complete and detailed answer to the question " What compiler do when it see the name 'A'

Drools - Ability to define rules at runtime?

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问题 It is possible to define rules dynamically completely at runtime ? Also change the ruleset at runtime. For example, at time = t_1 the ruleset is { R1, R2, R3 } at time = t_2 the ruleset is { R1, R3, R4 } ..... R1, R2 are rules that are defined at runtime. Thanks. 回答1: Yes, Drools is completely dynamic. You can add/remove/replaces rules at runtime. All the existing sessions are automatically updated in order to keep consistency. Check the documentation/javadoc: http://www.jboss.org/drools

What Rules does compiler have to follow when dealing with volatile memory locations?

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问题 I know when reading from a location of memory which is written to by several threads or processes the volatile keyword should be used for that location like some cases below but I want to know more about what restrictions does it really make for compiler and basically what rules does compiler have to follow when dealing with such case and is there any exceptional case where despite simultaneous access to a memory location the volatile keyword can be ignored by programmer. volatile SomeType *