NSPredicate具有多个参数和“AND行为” [英] NSPredicate with multiple arguments and "AND behaviour"

问题描述

我有一个函数从特定实体中获取满足指定条件的那些对象：

I have a function which fetches those objects from a particular entity that fulfill a specified criterion:

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，它似乎创建了像这样的查询：

When I pass an array with multiple aguments (multiple attribute names and values) it seems that creates a query like this:

attributeName1 = value1 OR attributeName2 = value2 OR attributeName3 = value3 OR...

我想更改AND的这些OR。

I would like to change these ORs for ANDs.

编辑：

问题在于它只是更换带有％K ==％@的前两项。

所以，我必须创建一个 NSCompoundPredicate动态创建谓词。

So, I have to create a NSCompoundPredicate to create a predicate dynamically.

推荐答案

创建谓词（具有可变数量的表达式）dyn通常，使用 NSCompoundPredicate ，例如

To create a predicate (with a variable number of expressions) dynamically, use NSCompoundPredicate, e.g.

let predicate = NSCompoundPredicate(andPredicateWithSubpredicates: subPredicates)

其中 subPredicates 是 [NSPredicate] 数组，每个子预测
都是从循环中提供的参数创建的，其中

where subPredicates is a [NSPredicate] array, and each subpredicate is created from the provided arguments in a loop with

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 == %@", key, value)
        subPredicates.append(subPredicate)
    }

    let fetchRequest = NSFetchRequest(entityName: entityName)
    fetchRequest.predicate = NSCompoundPredicate(andPredicateWithSubpredicates: subPredicates)

    // ...
}

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