[英]How to fetch data from mongodB in Scala
我编写了以下代码以从MongoDB中获取数据
import com.typesafe.config.ConfigFactory
import org.mongodb.scala.{ Document, MongoClient, MongoCollection, MongoDatabase }
import scala.concurrent.ExecutionContext
object MongoService extends Service {
val conf = ConfigFactory.load()
implicit val mongoService: MongoClient = MongoClient(conf.getString("mongo.url"))
implicit val mongoDB: MongoDatabase = mongoService.getDatabase(conf.getString("mongo.db"))
implicit val ec: ExecutionContext = ExecutionContext.global
def getAllDocumentsFromCollection(collection: String) = {
mongoDB.getCollection(collection).find()
}
}
但是,当我尝试从getAllDocumentsFromCollection
获取数据时, getAllDocumentsFromCollection
没有获取每个数据以进行进一步处理。 相反,我越来越
FindObservable(com.mongodb.async.client.FindIterableImpl@23555cf5)
更新:
object MongoService {
// My settings (see available connection options)
val mongoUri = "mongodb://localhost:27017/smsto?authMode=scram-sha1"
import ExecutionContext.Implicits.global // use any appropriate context
// Connect to the database: Must be done only once per application
val driver = MongoDriver()
val parsedUri = MongoConnection.parseURI(mongoUri)
val connection = parsedUri.map(driver.connection(_))
// Database and collections: Get references
val futureConnection = Future.fromTry(connection)
def db1: Future[DefaultDB] = futureConnection.flatMap(_.database("smsto"))
def personCollection = db1.map(_.collection("person"))
// Write Documents: insert or update
implicit def personWriter: BSONDocumentWriter[Person] = Macros.writer[Person]
// or provide a custom one
def createPerson(person: Person): Future[Unit] =
personCollection.flatMap(_.insert(person).map(_ => {})) // use personWriter
def getAll(collection: String) =
db1.map(_.collection(collection))
// Custom persistent types
case class Person(firstName: String, lastName: String, age: Int)
}
我试图在上面的代码中也使用createPerson
但是我无法使其适用于getAll
并在createPerson
得到以下错误 请提出如何从集合中获取所有数据的建议。
对于OP来说,这可能为时已晚,但是希望以下使用mongo-spark检索和迭代集合的方法可以证明对其他人有用。
异步方式 -异步遍历文档意味着您不必将整个集合存储在内存中,这对于大型集合可能变得不合理。 但是,您将无法访问subscribe
代码块之外的所有文档以进行重用。 如果可以的话,我建议异步执行操作,因为这是打算使用mongo-scala驱动程序的方式。
db.getCollection(collectionName).find().subscribe(
(doc: org.mongodb.scala.bson.Document) => {
// operate on an individual document here
},
(e: Throwable) => {
// do something with errors here, if desired
},
() => {
// this signifies that you've reached the end of your collection
}
)
“同步”方式 -这是我的用例要求同步解决方案时使用的一种模式,并且正在使用较小的集合或结果集。 它仍然使用异步mongo-scala驱动程序,但是它返回文档列表并阻止下游代码执行,直到返回所有文档。 处理错误和超时可能取决于您的用例。
import org.mongodb.scala._
import org.mongodb.scala.bson.Document
import org.mongodb.scala.model.Filters
import scala.collection.mutable.ListBuffer
/* This function optionally takes filters if you do not wish to return the entire collection.
* You could extend it to take other optional query params, such as org.mongodb.scala.model.{Sorts, Projections, Aggregates}
*/
def getDocsSync(db: MongoDatabase, collectionName: String, filters: Option[conversions.Bson]): ListBuffer[Document] = {
val docs = scala.collection.mutable.ListBuffer[Document]()
var processing = true
val query = if (filters.isDefined) {
db.getCollection(collectionName).find(filters.get)
} else {
db.getCollection(collectionName).find()
}
query.subscribe(
(doc: Document) => docs.append(doc), // add doc to mutable list
(e: Throwable) => throw e,
() => processing = false
)
while (processing) {
Thread.sleep(100) // wait here until all docs have been returned
}
docs
}
// sample usage of 'synchronous' method
val client: MongoClient = MongoClient(uriString)
val db: MongoDatabase = client.getDatabase(dbName)
val allDocs = getDocsSync(db, "myCollection", Option.empty)
val someDocs = getDocsSync(db, "myCollection", Option(Filters.eq("fieldName", "foo")))
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