如何解决如何判断谓词coreData对象是否为空
我想用谓词过滤器判断coreData对象是否为空,因此可以从Web服务器或本地获取该对象。
struct MyView: View {
@AppStorage("filter") private var filter = ""
@Environment(\.managedObjectContext) var moc
@State private var valueFilter = ""
var body: some View {
FilterValueView(filter: valueFilter)
.onAppear(perform: fetchValues)
}
func fetchValues() {
// Set the value filter by valueFilter
self.valueFilter = self.filter
// Check if the values is fetched from web server
// If empty fetch from web server,if not fetch locally.
// How to do it?
}
}
struct FilterValueView: View {
var fetchRequest: FetchRequest<Value>
var values: FetchedResults<Value> { fetchRequest.wrappedValue }
var body: some View {
List(values,id: \.self) { value in
...
}
}
init(filter: String) {
fetchRequest = FetchRequest<Value>(entity: Value(),sortDescriptors: [],predicate: NSPredicate(format: "value filter is %@",filter))
}
}
解决方法
宁愿将其放在 select * from
crosstab('
select current_turbine_status,count(*) current_turbine_status
from wpv.v_master_data_turbine
group by current_turbine_status
having count(*) >1 ')as t("LinkDown" text,"Stop" text,"RUN" text)
中,因为获取的数据的结果将包含在其中,所以
FilterValueView
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