使用 NSExpression 构建的嵌套子查询崩溃但不是它的谓词

Question

我有一些代码可以使用 NSComparisonPredicate 和 NSExpression 递归构建嵌套子查询。这是平坦的时候：

    // Nested subquery
    let entityPath = NSExpression(forKeyPath: "$s.mainUserResult.operations")
    let subQueryExpression = NSExpression(forSubquery: entityPath, usingIteratorVariable: "t", predicate: NSPredicate(format: "$t.operationType == 3"))
    let countSubQuery = NSExpression(format: "%@.@count", argumentArray: [subQueryExpression])
    let p1 = NSComparisonPredicate(leftExpression: countSubQuery,
                                 rightExpression: NSExpression(forConstantValue: 0),
                                 modifier: .direct,
                                 type: .greaterThan,
                                 options: NSComparisonPredicate.Options(rawValue: 0))

    // Main subquery
    let entityPath2 = NSExpression(forKeyPath: "sessions")
    let subQueryExpression2 = NSExpression(forSubquery: entityPath2, usingIteratorVariable: "s", predicate: p1)
    let countSubQuery2 = NSExpression(format: "%@.@count", argumentArray: [subQueryExpression2])
    
    let p2 = NSComparisonPredicate(leftExpression: countSubQuery2,
                                 rightExpression: NSExpression(forConstantValue: 0),
                                 modifier: .direct,
                                 type: .greaterThan,
                                 options: NSComparisonPredicate.Options(rawValue: 0))

当我获取一些实体时，上述代码崩溃并出现以下错误：

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Can't have a non-relationship collection element in a subquerySUBQUERY($s.mainUserResult.operations, $t, $t.operationType == 3)'

真正奇怪的是，当我通过复制 NSComparisonPredicate 的结果 predicateFormat 手动构建谓词时，它确实有效！

使用谓词 p2 获取会导致错误，而使用结果格式获取则有效：

   let p2 = NSPredicate(format: "SUBQUERY(sessions, $s, SUBQUERY($s.mainUserResult.operations, $t, $t.operationType == 3).@count > 0).@count > 0")

如何使 NSComparisonPredicate 工作？

Answer 1

NSExpression(forKeyPath: "$s.mainUserResult.operations")

会

self.value(forKeyPath: "$s.mainUserResult.operations")

这应该是

s.value(forKeyPath: "mainUserResult.operations")

表达式：

NSExpression(format: "$s.mainUserResult.operations", argumentArray: [])

使用 NSExpression 构建的嵌套子查询崩溃但不是它的谓词

Nested subqueries built with NSExpression crashes but not its predicate

swift

core-data

subquery

nspredicate

nsexpression