FS2 运行 按顺序流

Question

我有一个相当简单的用例。我有两个 Web 服务调用，一个获取产品，另一个获取关系。我想 运行 fetchProducts() 首先从产品集中提取一个字段，然后将输出传递给 fetchRelationships(ids: Seq[String])，这样我就可以在产品上重新设置关系。这是代码：

def fetchProducts(): Stream[IO, Seq[Product]]= {
 //webservice call
}

def fetchRelationship(ids: Seq[Product]): Stream[IO, Seq[Relationship]] = {
 //webservice call
}

//Pseudocode. How can I do this with fs2 Streams?
def process = {
      val prods = fetchProducts() //run this first
      val prodIds = prods.flatMap(i => i.productId)
      val rels = fetchRelationships(prodIds) //run after all all products are fetched 
      prods.forEach(p => p.setRelation(rels.get(p.id))
    }
}

 case class Product(productId: Option[String],
                        name: Option[String],
                        description: Option[String],
                        brandName: Option[String])

我受制于外部Api无法批量获取结果。所以我不确定如何使用 fs2 来表达它，或者我是否应该使用它。

Answer 1

不幸的是，您在问题中的代码与您的文字描述不符，并且遗漏了很多重要的部分（例如整个 Relationship class）。也不清楚

I am constrained by the external Api to get the results in batches

确实是这个意思。也不清楚为什么 Product 中的所有字段包括 productId 都是 Option.

以下代码可以编译，可能是也可能不是您需要的代码：

case class Product(productId: Option[String],
                   name: Option[String],
                   description: Option[String],
                   brandName: Option[String],
                   relationships: mutable.ListBuffer[Relationship]) {

}

case class Relationship(productId: String, someInfo: String)

def fetchProducts(): Stream[IO, Seq[Product]] = {
  //webservice call
  ???
}

//    def fetchRelationships(ids: Seq[Product]): Stream[IO, Seq[Relationship]] = {
def fetchRelationships(ids: Seq[String]): Stream[IO, Seq[Relationship]] = {
  //webservice call
  ???
}

def process():  = {
  val prods = fetchProducts() //run this first
  val prodsAndRels: Stream[IO, (Seq[Product], Seq[Relationship])] = prods.flatMap(ps => fetchRelationships(ps.map(p => p.productId.get)).map(rs => (ps, rs)))

  val prodsWithFilledRels: Stream[IO, immutable.Seq[Product]] = prodsAndRels.map({ case (ps, rs) => {
    val productsMap = ps.map(p => (p.productId.get, p)).toMap
    rs.foreach(rel => productsMap(rel.productId).relationships += rel)
    ps.toList
  }
  })
  prodsWithFilledRels
}