Following the comments on Mongoose: how to define a combination of fields to be unique?
First let's get the array of data sorted by all values which supposed to be unique.
Assuming we're talking about strings (as in this question), we can combine them to create one long string that is supposed to be unique.
Being sorted, if there are duplicate values they'll show up right after the other, so let's look for results that repeat themselves:
var previousName;
Person.find().sort('firstName lastName').exec().each(function (person) {
var name = person.firstName + person.lastName;
if (name == previousName) {
console.log(name);
person.remove();
}
previousName = name;
})
I need to return a list of objects along with a count of its related objects. It doesn't seem to be possible to do this in a single dictionary fetch request as I am unable to group the fetch results by objectID.
let objectIDExpression = NSExpressionDescription()
objectIDExpression.name = "objectID"
objectIDExpression.expression = NSExpression.expressionForEvaluatedObject()
objectIDExpression.expressionResultType = NSAttributeType.ObjectIDAttributeType
let countExpression = NSExpressionDescription()
countExpression.name = "count"
countExpression.expression = NSExpression(forFunction: "count:", arguments: [NSExpression(forKeyPath: "entries")])
countExpression.expressionResultType = .Integer32AttributeType
let fetchRequest = NSFetchRequest(entityName: "Tag")
fetchRequest.resultType = .DictionaryResultType
fetchRequest.propertiesToFetch = [objectIDExpression, countExpression]
fetchRequest.propertiesToGroupBy = [objectIDExpression]
var error: NSError?
if let results = self.context.executeFetchRequest(fetchRequest, error: &error) {
println(results)
}
When this request executes it errors with:
'Invalid keypath expression ((<NSExpressionDescription: 0x7f843bf2d470>), name objectID, isOptional 1, isTransient 0, entity (null), renamingIdentifier objectID, validation predicates (
), warnings (
), versionHashModifier (null)
userInfo {
}) passed to setPropertiesToFetch:'
I also tested just passing the "objectID" expression name, but that also fails.
Is there therefore no way to group by object ID?
You can get the required count without using propertiesToGroupBy. CoreData seems to infer the correct scope for the count and uses a sub-SELECT instead (strangely, only if the fetch includes an attribute as well as the objectID and count, see below). For example, I have Tag many-many with Items:
First attempt
I can fetch tagName and the count of items as follows:
NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:#"Tag"];
NSExpressionDescription *countED = [NSExpressionDescription new];
countED.expression = [NSExpression expressionWithFormat:#"count:(items)"];
countED.name = #"countOfItems";
countED.expressionResultType = NSInteger64AttributeType;
fetch.resultType = NSDictionaryResultType;
fetch.propertiesToFetch = #[#"tagName", countED];
NSArray *results = [self.context executeFetchRequest:fetch error:nil];
NSLog(#"results is %#", results);
which generates the following SQL:
SELECT t0.ZTAGNAME, (SELECT COUNT(t1.Z_3ITEMS) FROM Z_3TAGS t1 WHERE (t0.Z_PK = t1.Z_8TAGS) ) FROM ZTAG t0
Second attempt
Sadly, it seems CoreData gets confused if I try to select the objectID instead of the tagName:
NSExpressionDescription *selfED = [NSExpressionDescription new];
selfED.expression = [NSExpression expressionForEvaluatedObject];
selfED.name = #"self";
selfED.expressionResultType = NSObjectIDAttributeType;
fetch.resultType = NSDictionaryResultType;
fetch.propertiesToFetch = #[selfED, countED];
generates this SQL:
SELECT t0.Z_ENT, t0.Z_PK, COUNT( t1.Z_3ITEMS) FROM ZTAG t0 LEFT OUTER JOIN Z_3TAGS t1 ON t0.Z_PK = t1.Z_8TAGS
which counts all the rows from the outer join (and suggests that you need to group by the objectID, though we know that won't work).
Final attempt
However, include tagName and objectID, and all is well again:
fetch.propertiesToFetch = #[selfED, #"tagName", countED];
gives:
SELECT t0.Z_ENT, t0.Z_PK, t0.ZTAGNAME, (SELECT COUNT(t1.Z_3ITEMS) FROM Z_3TAGS t1 WHERE (t0.Z_PK = t1.Z_8TAGS) ) FROM ZTAG t0
which seems to do the trick. (Sorry for reverting to Objective-C, and for using different entity/attribute names, but I'm sure you get the picture).
Aside
One other curiosity I discovered is that the second attempt above can also be made to work by counting an attribute of the relationship, rather than the relationship itself:
countED.expression = [NSExpression expressionWithFormat:#"count:(items.itemName)"];
fetch.propertiesToFetch = #[selfED, countED];
gives:
SELECT t0.Z_ENT, t0.Z_PK, (SELECT COUNT(t2.ZITEMNAME) FROM Z_3TAGS t1 JOIN ZITEMS t2 ON t1.Z_3ITEMS = t2.Z_PK WHERE (t0.Z_PK = t1.Z_8TAGS) ) FROM ZTAG t0
which will (I think) give the correct counts provided itemName is not nil.
I played with this for a bit, sure there had to be some way to tell core-data to group by the primary key.
I couldn't figure it out, though I believe it to be possible.
The best I could do was add another unique attribute "uuid" (which I use for all of my entities anyway, for various reasons). You can do this easily enough with NSUUID, or you can take the permanent object ID URI representation and turn it into a string.
Anyway, I think this gives you what you want, but does so by requiring a separate unique attribute.
fetchRequest.propertiesToGroupBy = #[#"uuid"];
I tried a bunch of alternatives as the group-by property but expressionForEvaluatedObject always barfs, and other attempts fell flat.
I'm sure you know this already. Just in case, though it's at least a workaround, even if you don't use it for anything else, until someone comes around who has actually done this before.
FWIW, here is the SQL...
CoreData: sql: SELECT t0.Z_ENT, t0.Z_PK, COUNT( t1.Z_1ENTRIES), t0.ZUUID
FROM ZTAG t0 LEFT OUTER JOIN Z_1TAGS t1 ON t0.Z_PK = t1.Z_2TAGS
GROUP BY t0.ZUUID
Surely, there has to be a way to tell it to substitute t0.Z_PK in the group-by clause. I would image that should be an easy special case for expressionForEvaluatedObject or "objectID" or "self" or "self.objectID"
Good luck, and please report back if you solve it. I'd be very interested.
It is perhaps easier to use a NSFetchedResultsController. You can set the sectionNameKeyPath to group and use the resulting NSIndexPaths to construct your dictionary.
That being said, I do not think that it makes any sense to group by objectID because every object ID is by definition unique. So there will be one instance in each group. This is likely why setting propertiesToGroupBy fails.
So, short answer: no.
E.g.
let fetchRequest = NSFetchRequest(entityName: "Tag")
var output = [(NSManagedObjectID, Int)]()
do {
let results = try context.executeFetchRequest(request) as! [Tag]
for tag in results {
output.append((tag.objectID, tag.entries.count))
}
} catch {}
// output contains tuples with objectID and count
If entriesis optional, use tag.entries?.count ?? 0.
I have one CoreData record that contains all of the app's settings. When I read that single record (using MagicalRecord), I get an array back. My question is: can I get addressabiltiy to the individual fields in the record without using "[0]" (field index), but rather using [#"shopOpens"]?
I was thinking something like this, but I don't think it's right:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"aMostRecentFlag == 1"]; // find old records
preferenceData = [PreferenceData MR_findAllWithPredicate:predicate inContext:defaultContext]; // source
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
NSMutableDictionary *preferencesDict = [[userDefaults dictionaryForKey:#"preferencesDictionary"] mutableCopy]; // target
// start filling the userDefaults from the last Preferences record
/*
Printing description of preferencesDict: {
apptInterval = 15;
colorScheme = Saori;
servicesType = 1;
shopCloses = 2000;
shopOpens = 900;
showServices = 0;
syncToiCloud = 0;
timeFormat = 12;
}
*/
[preferencesDict setObject: preferenceData.colorScheme forKey:#"shopOpens"];
UPDATE
This is how I finally figured it out, for those who have a similar question:
NSPredicate *filter = [NSPredicate predicateWithFormat:#"aMostRecentFlag == 0"]; // find old records
NSFetchRequest *freqest = [PreferenceData MR_requestAllWithPredicate: filter];
[freqest setResultType: NSDictionaryResultType];
NSDictionary *perferenceData = [PreferenceData MR_executeFetchRequest:freqest];
Disclaimer: I've never used magical record, so the very first part is just an educated guess.
I imagine that preferenceData is an instance of NSArray firstly because the method name uses findAll which indicates that it will return multiple instances. Secondly, a normal core data fetch returns an array, and there is no obvious reason for that find method to return anything different. Thirdly, you referenced using an index operation in your question.
So, preferenceData is most likely an array of all objects in the store that match the specified predicate. You indicated that there is only one such object, which means you can just grab the first one.
PreferenceData *preferenceData = [[PreferenceData
MR_findAllWithPredicate:predicate inContext:defaultContext] firstObject];
Now, unless it is nil, you have the object from the core data store.
You should be able to reference it in any way you like to access its attributes.
Note, however, that you can fetch objects from core data as dictionary using NSDictionaryResultType, which may be a better alternative for you.
Also, you can send dictionaryWithValuesForKeys: to a managed object to get a dictionary of specific attributes.
How to get the number of RDF resources (subjects) associated with a specific property?
I don't want to use the list statements iterator to count the number of unique resources because this will also count the number of statements with the same subjects but different objects. Isn't there just a method that just returns the number of unique subjects of a particular property?
StmtIterator iter = model1.listStatements();
// print out the predicate, subject and object of each statement
int u=0;
while (iter.hasNext()) {
Statement stmt = iter.nextStatement(); // get next statement
Resource subject = stmt.getSubject(); // get the subject
Property predicate = stmt.getPredicate(); // get the predicate
RDFNode object = stmt.getObject();
u++;
}
One of Model.listResourcesWithProperty operations.
Model javadoc
I am using the ArangoDB java driver and am trying to query for documents containing one of a number of Strings, which are stored in the arangoDB documents in lists. I am using ArrayList with a list of Strings in the query.
Query:
FOR document IN documents FILTER ( #now - document.dateAdded < 2592000000 ) &&
(document.categories IN #categories || document.tags IN #tags
|| document.locations IN #locations ) RETURN document
Map<String, Object> bindVars = new MapBuilder().put("now", now).put("categories", categories).put("#tags", tags).put("#locations", locations).get();
"now" contains a long. All the others are ArrayList<String>. This is throwing an error explaining that "bind parameter '#tags' has an invalid value or type". Since this ArrayList is no different than the others, my only theory is that I am inputting the logic incorrectly. How does one query for:
FunctionCondition1 AND (condition2 OR condition3 OR condition4)
The bind vars are marked in the query using '#', but they are given without the first '#'. A collection parameter is specified with two at symbols ## as ##myvariablecollection. In this case the bind var is #myvariablecollection and must be of type collection.
For example:
FOR a IN ##collection FILTER a.x == #now RETURN a
requires the bind variables to be given as #collection and now where #collection must name a collection and now should be (in this example) a number.
Map<String, Object> bindVars = new MapBuilder().put("#collection", "myCollection").put("now", 1234).get();