const admin = require("firebase-admin");
const firestore = admin.firestore();

exports.bucketTesting = functions.https.onRequest(async (req, res) => {

  //code to source file.metadata.mediaLink

  const imagesRef = firestore.collection("images");
  
  // the following will return an array 
  const specificImages = (await imagesRef
    .where("imageUrl", "==", file.metadata.mediaLink)
    .get()).docs.map(each => each.data()) || [];
    
    
  /* the console log on the next line will show the array
  it will show multiple items if there is more than one document
  where imageUrl === file.metadata.mediaLink */
  console.log(specificImages);
  
  /* all is left to do is to return the array 
    or return a single document */
    
  // the following is the case when you are just returning a single document
  res.send({
    desiredData: specificImages?.[0] ?? {} // fallback if there is no document
  })
}

您的意见：“如何获取文档或docID？“

您的代码正确，可以获取文档docID和数据，但如注解中所述，查询返回0个文档。

由于您确定只有一个文档对应于查询，因此您可以做的唯一调整是使用docs数组，如下所示：

exports.bucketTesting = functions.https.onRequest(async (req, res) => {

  const imagesRef = firestore.collection("images");
  const querySnapshot = await imagesRef
          .where("imageUrl", "==", file.metadata.mediaLink)
          .get();

  if (querySnapshot.size === 0) {
     // No document found
     // Send back a message or an error
     res.status(500).send("No document found");
  } else {
     const uniqueDocSnapshot = querySnapshot.docs[0];
     console.log(uniqueDocSnapshot.id, "=>", uniqueDocSnapshot.data());

     res.send(...);
  }

        

})