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问题 I have a person entity containing an Address as a value object: public Person() { WithTable("Person"); Id(x => x.Id); Component<Address>(x => x.Address, a => { a.Map(x => x.Address1); a.Map(x => x.Address2); a.Map(x => x.Address3); a.Map(x => x.Town); a.Map(x => x.Postcode); }); } It states in the NHibernate docs that if all the properties of a value object (Address1, Address2 etc) are null, the entire component will be mapped as null (i.e. Person.Address will be null). This is giving me

问题 This question already has answers here : When can argv[0] have null? (4 answers) Closed 2 years ago . In the data structures class that I am currently taking, we have been tasked with writing a web crawler in C++. To give us a head start, the professor provided us with a program to get the source from a given URL and a simple HTML parser to strip the tags out. The main function for this program accepts arguments and so uses argc/argv. The code used to check for the arguments is as follows: //

问题 I have an array of JSON objects. To parse these arrays and store the simply data type values, I have to make assumptions of the key names and store them accordingly. I also know that sometimes the key's values will be null. example {["promotion":null]} how would I parse this? If I try to access a key whose value is null, I get a JSONException. Now this makes sense, but even if I do if(myJSObject.getString("promotion")!=null) then I will still get JSON exception when it checks how would I do a

问题 What is the best way to determine whether an object reference variable is null ? Is it the following? MyObject myObjVar = null; if (myObjVar == null) { // do stuff } 回答1: Yes, you are right, the following snippet is the way to go if you want to execute arbitrary code: MyObject myObjVar; if (myObjVar == null) { // do stuff } BTW: Your code wouldn't compile the way it is now, because myObjVar is accessed before it is being initialized. 回答2: The way you are doing is the best way if (myObjVar ==

问题 { "abc": null, "def": 9 } I have JSON data which looks like this. If not for null (without quotes as a string), I could have used ast module's literal_eval to convert the above to a dictionary. A dictionary in Python cannot have null as value but can have "null" as a value. How do I convert the above to a dictionary that Python recognizes? 回答1: You should use the built-in json module, which was designed explicitly for this task: >>> import json >>> data = ''' ... { ... "abc": null, ... "def":

问题 I have a list with dictionaries in which I sort them on different values. I'm doing it with these lines of code: def orderBy(self, col, dir, objlist): if dir == 'asc': sorted_objects = sorted(objlist, key=lambda k: k[col]) else: sorted_objects = sorted(objlist, key=lambda k: k[col], reverse=True) return sorted_objects Now the problem is that I occasionally have null values or empty strings when I try to sort and then it all breaks down. I'm not sure but i think that this is the exception that

问题 I have a page where you register your dog, and I want all these fields to be required: $required_fields = array('name', 'age', 'gender', 'breed', 'size'); foreach ($_POST as $key => $value) { if (empty($value) && in_array($key, $required_fields) === true) { $errors[] = 'All fields marked with * are required.'; break 1; } } The problem is, that if someone enters 0 (which I instruct them to do if the dog is a puppy), the submission seems to read that field as empty (giving me this error). I

问题 How to assign nil to an object in Swift. I'm getting error if assigned directly. 回答1: From Apple Documentation: nil cannot be used with nonoptional constants and variables . If a constant or variable in your code needs to work with the absence of a value under certain conditions, always declare it as an optional value of the appropriate type also very importante to notice: Swift’s nil is not the same as nil in Objective-C . In Objective-C, nil is a pointer to a nonexistent object. In Swift,

问题 In my MySQL table, every column by itself can be NULL, but there must be at least one column with a non-NULL value. At the moment, I am wrapping an insert statement in a stored procedure which prevents insertion of all-NULL rows, but that of course does not keep anyone from using native INSERT statements, circumventing my wrapper procedure. Is there a 'native' way to define the table with that constraint ? 回答1: Since MySQL doesn't enforce check constraints, you may want to emulate one with a

问题 Can someone help me with this error? NoMethodError in Posts#create Showing C:/Users/User/Documents/website/app/views/posts/_form.html.erb where line #24 raised: undefined method `collect' for nil:NilClass Extracted source (around line #24): 23: <%= f.label :categoria %> 24: <%= f.select :categoria_id, @categoria.collect { |c| [ c.name, c.id ] } %> Trace of template inclusion: app/views/posts/new.html.erb My _form.html.erb <%= form_for(@post, :html => { :multipart => true }) do |f| %> <% if