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问题 This question already has answers here : Check if property is set in Core Data? (2 answers) Closed 4 years ago . I have a UITableViewController loading its entries from Core Data via a NSFetchedResultsController . Like this: let historyItem = fetchedResults.objectAtIndexPath(indexPath) as HistoryItem historyItem has a title property defined like this: @NSManaged var title: String So in cellForRowAtIndexPath the code says cell?.textLabel?.text = historyItem.title and that should all be fine.

问题 There is a tweet from Jared Parsons who is c# compiler developer. The tweet claims that we should use "is object" as non null check. My question is why exactly is that and if I'm getting result from call to service should I run "is object" check instead of "!= null"? From my understanding and what I can see in Microsoft documentation "is" keyword should be used as type check. I wasn't able to find "is object" as non null check example anywhere in Microsoft documentation that's why it concerns

问题 Its great when you can return a null/empty object in most cases to avoid nulls, but what about Collection like objects? In Java, Map returns null if key in get(key) is not found in the map. The best way I can think of to avoid null s in this situation is to return an Entry<T> object, which is either the EmptyEntry<T> , or contains the value T . Sure we avoid the null , but now you can have a class cast exception if you don't check if its an EmptyEntry<T> . Is there a better way to avoid null

问题 Due to reputation constraints, this is a follow-up question to this answer to a prior question. I'd like to know if there's a more efficient way to test each field for changes while handling NULL values. CREATE TABLE foo ( a INT NULL DEFAULT NULL, b INT NULL DEFAULT NULL, c INT NULL DEFAULT NULL ); CREATE TABLE bar ( a INT NULL DEFAULT NULL, b INT NULL DEFAULT NULL, c INT NULL DEFAULT NULL ); INSERT INTO foo (a, b) VALUES (1, 2); I want a trigger whose actions occur after update only if a

问题 I have this Java class in a Jar file included as a dependency of an Scala program (like the Axis jar): class MyClass { private String[] someStrings; public String[] getSomeStrings() { return someStrings; } } In my Scala program I have a Java API that return an instance of MyClass instance of MyClass to my program in Scala: val myInstance = JavaAPI.getInstanceOfMyClass() Then I try to use the someStrings array in my Scala program but it's null (let say that it wasn't properly initialized) for

问题 Please have a look at the database design below: create table Person (id int identity, InvoiceID int not null) create table Invoice (id int identity, date datetime) Currently all persons have an invoiceID i.e. the InvoiceID is not null . I want to extend the database so that some person does not have an Invoice . The original developer hated nulls and never uses them. I want to be consistent so I am wondering if there are other patterns I can use to extend the database to meet this

问题 I am working on an app that reads QR codes and I need the orientation of the code. The ZXING source states that the orientation can be obtained from a hashtable ResultMetaData through the key ORIENTATION Now, my issue is that the getResultMetaData() is not returning any results when I run the following: orientation = (Integer) Returned[v].getResultMetadata().get("ORIENTATION"); However, the line directly above this, points = Returned[v].getResultPoints(); Works just fine, so I know that the

问题 After a join by ID, my data frame looks as follows: ID | Features | Vector 1 | (50,[...] | Array[1.1,2.3,...] 2 | (50,[...] | Null I ended up with Null values for some IDs in the column 'Vector'. I would like to replace these Null values by an array of zeros with 300 dimensions (same format as non-null vector entries). df.fillna does not work here since it's an array I would like to insert. Any idea how to accomplish this in PySpark? ---edit--- Similarly to this post my current approach: df

问题 I have multiple, large, csv files, each of which has missing values in many places. When I import the csv file into SQLite, I would like to have the missing values recorded as NULL for the reason that another application expects missing data to be indicated by NULL. My current method does not produce the desired result. An example CSV file (test.csv) is: 12|gamma|17|delta 67||19|zeta 96|eta||theta 98|iota|29| The first line is complete; each of the other lines has (or is meant to show!) a

问题 I have a Log file in which i need to store data with REGEX. I tried below query but loading all NULL values. I have checked REGEX with http://www.regexr.com/, its working fine for my data. CREATE EXTERNAL TABLE IF NOT EXISTS avl(imei STRING,packet STRING) ROW FORMAT SERDE 'org.apache.hadoop.hive.contrib.serde2.RegexSerDe' WITH SERDEPROPERTIES ( "input.regex" = "(IMEI\\s\\d{15} (\\b(\\d{15})([A-Z0-9]+)) )", "output.format.string" = "%1$s %2$s" ) STORED AS TEXTFILE; LOAD DATA INPATH 'hdfs:/user