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问题 I looked for documentation of how to perform $out in an aggregation but I didn't find. This is my query: Top.aggregate([ {$sort: {created: -1}}, {$group: {_id:'$location', title:{$push: '$title'}}}, {$project: {location: '$location', mostRecentTitle: '$title'}}, {$out: "aggr_out"} ]).exec(function(err, docs) { console.log(docs); console.log(err) }); Schema: var schema = mongoose.Schema({ location: {type: String}, title: {type: String}, created: {type: Number, default: Math.floor(new Date() /

问题 I'm unclear as to why the following code snippet isn't covarient? public interface IResourceColl<out T> : IEnumerable<T> where T : IResource { int Count { get; } T this[int index] { get; } bool TryGetValue( string SUID, out T obj ); // Error here? } Error 1 Invalid variance: The type parameter 'T' must be invariantly valid on 'IResourceColl.TryGetValue(string, out T)'. 'T' is covariant. My interface only uses the template parameter in output positions. I could easily refactor this code to

问题 I'm unclear as to why the following code snippet isn't covarient? public interface IResourceColl<out T> : IEnumerable<T> where T : IResource { int Count { get; } T this[int index] { get; } bool TryGetValue( string SUID, out T obj ); // Error here? } Error 1 Invalid variance: The type parameter 'T' must be invariantly valid on 'IResourceColl.TryGetValue(string, out T)'. 'T' is covariant. My interface only uses the template parameter in output positions. I could easily refactor this code to

问题 I am trying to write a unit test for a method that has out parameters. My method specifically is a TryParse method for my custom object. I am using .NET 4.5/5 with Visual Studio 2013. This allows me to fully realize private/internal and static objects using the PrivateType object. The one thing that seems to escape me is how to test for the out parameter as I cannot use this keyword in the InvokeStatic method. I am looking for the proper solution to test this architecture design. The use for

问题 I am trying to write a unit test for a method that has out parameters. My method specifically is a TryParse method for my custom object. I am using .NET 4.5/5 with Visual Studio 2013. This allows me to fully realize private/internal and static objects using the PrivateType object. The one thing that seems to escape me is how to test for the out parameter as I cannot use this keyword in the InvokeStatic method. I am looking for the proper solution to test this architecture design. The use for

问题 I am trying to write a unit test for a method that has out parameters. My method specifically is a TryParse method for my custom object. I am using .NET 4.5/5 with Visual Studio 2013. This allows me to fully realize private/internal and static objects using the PrivateType object. The one thing that seems to escape me is how to test for the out parameter as I cannot use this keyword in the InvokeStatic method. I am looking for the proper solution to test this architecture design. The use for

问题 this code works fine on emulator, but on real device it gives java.net.SocketException :the operation timed out ive got a php script running on my xampp server. package com.example.new1; import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.HttpURLConnection; import java.net.URL; import android.os.AsyncTask; import android.os.Bundle; import android.app.Activity; import android.view.Menu; import android.view.View; import android.widget.TextView; public class

问题 When a C# function has an output parameter, you make that clear as follows: private void f(out OutputParameterClass outputParameter); This states that the parameter does not have to be initialized when the function is called. However, when calling this function, you have to repeat the out keyword : f(out outputParameter); I am wondering what this is good for. Why is it necessary to repeat part of the function specification? Does anyone know? 回答1: It means you know what you're doing - that you

问题 I want to do a hbase scan with filters. For example, my table has column family A,B,C, and A has a column X. Some rows have the column X and some do not. How can I implement the filter to filter out all the rows with column X? 回答1: I guess you are looking for SingleColumnValueFilter in HBase. As mentioned in the API To prevent the entire row from being emitted if the column is not found on a row, use setFilterIfMissing(boolean) on Filter object. Otherwise, if the column is found, the entire

问题 today I saw a snipped that looked really horrible to me, but unfortunetly I cannot simply change it, so I wonder if I can bypass this somehow. I have a class with a constructor that has an output-parameter for success. But that looks really ugly to me. And now when deriving from this class I have to take this param with me- if I want to or not. class ClassA { ClassA(out bool success) {...} } class B: ClassA { // call the constructor from ClassA but without the out-param } So I´d know if its