我有一个函数从特定实体中获取满足指定标准的那些对象：
func fetchWithPredicate(entityName: String,argumentArray: [AnyObject]) -> [NSManagedObject] {
let fetchRequest = NSFetchRequest(entityName: entityName)
fetchRequest.predicate = NSPredicate(format: "%K == %@",argumentArray: argumentArray)
do {
return try self.managedContext.executeFetchRequest(fetchRequest) as! [NSManagedObject]
} catch {
let fetchError = error as NSError
print(fetchError)
return [NSManagedObject]()
}
}
当我传递一个包含多个aguments(多个属性名称和值)的数组时,似乎会创建一个这样的查询：
attributeName1 = value1 OR attributeName2 = value2 OR attributeName3 = value3 OR...
我想为AND更改这些OR.
编辑：
问题是它只有replacing the first two items,“％K ==％@”.
所以,我必须创建一个NSCompoundPredicate to create a predicate dynamically.
解决方法
要动态创建谓词(具有可变数量的表达式),请使用NSCompoundPredicate,例如
let predicate = NSCompoundPredicate(andPredicateWithSubpredicates: subPredicates)
其中subPredicates是[NSPredicate]数组,每个subpredicate
是从循环中提供的参数创建的
NSPredicate(format: "%K == %@",key,value)
像这样(未经测试)：
func fetchWithPredicate(entityName: String,argumentArray: [NSObject]) -> [NSManagedObject] {
var subPredicates : [NSPredicate] = []
for i in 0.stride(to: argumentArray.count,by: 2) {
let key = argumentArray[i]
let value = argumentArray[i+1]
let subPredicate = NSPredicate(format: "%K == %@",value)
subPredicates.append(subPredicate)
}
let fetchRequest = NSFetchRequest(entityName: entityName)
fetchRequest.predicate = NSCompoundPredicate(andPredicateWithSubpredicates: subPredicates)
// ...
}
