How to get item with max id?

问题

I'm tryig to get the ítem with max id using this query

realm.objects(Entity).filter("@max.id").first

It's throwing an error saying that can't parse query so it seems this is not the correct way to do it.

How can I write this query on Realm for Swift?

回答1:

Filters alone cannot do what you're after as they only consider a single top-level object at a time.

Beyond that conceptual issue, there are a few issues with the code you posted:

@"@max.id" is not a valid NSPredicate format string. NSPredicate format strings must be composed of comparisons between expressions, not expressions on their own.
Collection operators such as @max must be applied to a collection. In your example it is being applied to an Entity. Since an Entity is not a collection, the predicate would not be valid. It would be valid to apply a collection operator to a List property on Entity though.

Something like the following should do what you're after:

let entities = realm.objects(Entity)
let id = entities.max("id") as Int?
let entity = id != nil ? entities.filter("id == %@", id!).first : nil

回答2:

I'm using Xcode 8.0 and Swift 3.0

Following worked for me:

let allEntries = realm.objects(Model.self)
if allEntries.count > 0 {
    let lastId = allEntries.max(ofProperty: "id") as Int?
    return lastId! + 1
} else {
    return 1
}

回答3:

Swift 4 and Xcode 9.3

if let personWithMaxAge = realm.objects(Person.self).max(by: { $0.age > $1.age }) {
    print(personWithMaxAge.age)
}

来源：https://stackoverflow.com/questions/32804266/how-to-get-item-with-max-id

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ios

swift

realm