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samples: Add example snippets for stale reads #1273

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Original file line number Diff line number Diff line change
Expand Up @@ -20,13 +20,17 @@
import com.google.api.core.ApiFuture;
import com.google.api.core.ApiFutures;
import com.google.cloud.firestore.CollectionReference;
import com.google.cloud.firestore.DocumentReference;
import com.google.cloud.firestore.DocumentSnapshot;
import com.google.cloud.firestore.Firestore;
import com.google.cloud.firestore.Query;
import com.google.cloud.firestore.Query.Direction;
import com.google.cloud.firestore.QueryDocumentSnapshot;
import com.google.cloud.firestore.QuerySnapshot;
import com.google.cloud.firestore.TransactionOptions;
import com.google.cloud.firestore.WriteResult;
import com.google.protobuf.Timestamp;
import java.time.Instant;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
Expand Down Expand Up @@ -591,6 +595,50 @@ Query filterNotIn() {
return query;
}

/**
* Run stale reads. Demonstrate a document lookup and a query.
*
* @return DocumentSnapshot documentResult
*/
DocumentSnapshot runStaleReads() throws Exception {
// [START firestore_stale_read]
// Create a read time 15 seconds in the past
Instant now = Instant.now();
final int fifteenSeconds = 15;
final Timestamp readTime =
Timestamp.newBuilder()
.setSeconds(now.getEpochSecond() - fifteenSeconds)
.setNanos(now.getNano())
.build();

// Set transaction options. Use read-only and set read time
// Stale reads require a read-only transaction
TransactionOptions options =
TransactionOptions.createReadOnlyOptionsBuilder().setReadTime(readTime).build();

// Create a document reference
final DocumentReference documentReference = db.collection("cities").document("SF");

// Create a query against the cities collection.
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Query query = db.collection("cities").whereEqualTo("capital", true);

// run a transaction with the specified transaction options
ApiFuture<DocumentSnapshot> futureTransaction =
db.runTransaction(
transaction -> {
// Execute a stale read document lookup
final DocumentSnapshot documentResult = transaction.get(documentReference).get();

// Execute a stale read query
final QuerySnapshot queryResult = transaction.get(query).get();

return documentResult;
},
options);
// [END firestore_stale_read]
return futureTransaction.get();
}

/** Closes the gRPC channels associated with this instance and frees up their resources. */
void close() throws Exception {
db.close();
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@

import static com.google.common.collect.Sets.newHashSet;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotNull;
import static org.junit.Assert.assertTrue;

import com.example.firestore.BaseIntegrationTest;
Expand Down Expand Up @@ -271,6 +272,13 @@ public void testFilterNotIn() throws Exception {
assertEquals(expected, actual);
}

@Test
public void testSnapshotReads() throws Exception {
// Verify that this runs without error
DocumentSnapshot doc = queryDataSnippets.runStaleReads();
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assertNotNull("should not be null", doc);
}

private Set<String> getResultsAsSet(Query query) throws Exception {
List<String> docIds = getResults(query);
return new HashSet<>(docIds);
Expand Down
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