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Updated AndroidX
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M66B
239
app/src/main/java/androidx/room/LimitOffsetDataSource.java
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239
app/src/main/java/androidx/room/LimitOffsetDataSource.java
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/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package androidx.room.paging;
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import android.database.Cursor;
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import androidx.annotation.NonNull;
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import androidx.annotation.RestrictTo;
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import androidx.room.InvalidationTracker;
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import androidx.room.RoomDatabase;
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import androidx.room.RoomSQLiteQuery;
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import androidx.sqlite.db.SupportSQLiteQuery;
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import java.util.Collections;
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import java.util.List;
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import java.util.Set;
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import java.util.concurrent.atomic.AtomicBoolean;
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/**
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* A simple data source implementation that uses Limit & Offset to page the query.
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* <p>
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* This is NOT the most efficient way to do paging on SQLite. It is
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* <a href="http://www.sqlite.org/cvstrac/wiki?p=ScrollingCursor">recommended</a> to use an indexed
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* ORDER BY statement but that requires a more complex API. This solution is technically equal to
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* receiving a {@link Cursor} from a large query but avoids the need to manually manage it, and
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* never returns inconsistent data if it is invalidated.
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*
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* This class is used for both Paging2 and Pagin3 (via its compat API). When used with Paging3,
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* it does lazy registration for observers to be suitable for initialization on the main thread
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* whereas in Paging2, it will register observer eagerly to obey Paging2's strict Data Source
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* rules. (Paging2 does not let data source to possibly return invalidated data).
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*
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* @param <T> Data type returned by the data source.
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*
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* @hide
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*/
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@SuppressWarnings("deprecation")
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@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP_PREFIX)
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public abstract class LimitOffsetDataSource<T> extends androidx.paging.PositionalDataSource<T> {
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private final RoomSQLiteQuery mSourceQuery;
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private final String mCountQuery;
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private final String mLimitOffsetQuery;
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private final RoomDatabase mDb;
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@SuppressWarnings("FieldCanBeLocal")
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private final InvalidationTracker.Observer mObserver;
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private final boolean mInTransaction;
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private final AtomicBoolean mRegisteredObserver = new AtomicBoolean(false);
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protected LimitOffsetDataSource(@NonNull RoomDatabase db,
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@NonNull SupportSQLiteQuery query,
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boolean inTransaction,
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@NonNull
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String... tables) {
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this(db, RoomSQLiteQuery.copyFrom(query), inTransaction, tables);
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}
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protected LimitOffsetDataSource(
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@NonNull RoomDatabase db,
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@NonNull SupportSQLiteQuery query,
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boolean inTransaction,
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boolean registerObserverImmediately,
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@NonNull String... tables) {
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this(db, RoomSQLiteQuery.copyFrom(query), inTransaction, registerObserverImmediately,
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tables);
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}
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protected LimitOffsetDataSource(
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@NonNull RoomDatabase db,
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@NonNull RoomSQLiteQuery query,
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boolean inTransaction,
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@NonNull String... tables) {
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this(db, query, inTransaction, true /*register registerObserverImmediately*/, tables);
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}
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protected LimitOffsetDataSource(
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@NonNull RoomDatabase db,
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@NonNull RoomSQLiteQuery query,
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boolean inTransaction,
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boolean registerObserverImmediately,
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@NonNull String... tables) {
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mDb = db;
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mSourceQuery = query;
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mInTransaction = inTransaction;
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mCountQuery = "SELECT COUNT(*) FROM ( " + mSourceQuery.getSql() + " )";
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mLimitOffsetQuery = "SELECT * FROM ( " + mSourceQuery.getSql() + " ) LIMIT ? OFFSET ?";
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mObserver = new InvalidationTracker.Observer(tables) {
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@Override
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public void onInvalidated(@NonNull Set<String> tables) {
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invalidate();
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}
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};
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if (registerObserverImmediately) {
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registerObserverIfNecessary();
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}
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}
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private void registerObserverIfNecessary() {
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if (mRegisteredObserver.compareAndSet(false, true)) {
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mDb.getInvalidationTracker().addWeakObserver(mObserver);
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}
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}
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/**
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* Count number of rows query can return
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*
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* @hide
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*/
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@SuppressWarnings("WeakerAccess")
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public int countItems() {
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registerObserverIfNecessary();
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final RoomSQLiteQuery sqLiteQuery = RoomSQLiteQuery.acquire(mCountQuery,
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mSourceQuery.getArgCount());
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sqLiteQuery.copyArgumentsFrom(mSourceQuery);
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Cursor cursor = mDb.query(sqLiteQuery);
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try {
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if (cursor.moveToFirst()) {
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return cursor.getInt(0);
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}
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return 0;
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} finally {
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cursor.close();
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sqLiteQuery.release();
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}
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}
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@Override
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public boolean isInvalid() {
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registerObserverIfNecessary();
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mDb.getInvalidationTracker().refreshVersionsSync();
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return super.isInvalid();
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}
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@NonNull
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@SuppressWarnings("WeakerAccess")
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protected abstract List<T> convertRows(@NonNull Cursor cursor);
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@SuppressWarnings("deprecation")
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@Override
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public void loadInitial(@NonNull LoadInitialParams params,
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@NonNull LoadInitialCallback<T> callback) {
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registerObserverIfNecessary();
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List<T> list = Collections.emptyList();
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int totalCount;
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int firstLoadPosition = 0;
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RoomSQLiteQuery sqLiteQuery = null;
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Cursor cursor = null;
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mDb.beginTransaction();
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try {
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totalCount = countItems();
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if (totalCount != 0) {
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// bound the size requested, based on known count
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firstLoadPosition = computeInitialLoadPosition(params, totalCount);
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int firstLoadSize = computeInitialLoadSize(params, firstLoadPosition, totalCount);
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sqLiteQuery = getSQLiteQuery(firstLoadPosition, firstLoadSize);
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cursor = mDb.query(sqLiteQuery);
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List<T> rows = convertRows(cursor);
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mDb.setTransactionSuccessful();
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list = rows;
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}
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} finally {
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if (cursor != null) {
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cursor.close();
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}
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mDb.endTransaction();
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if (sqLiteQuery != null) {
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sqLiteQuery.release();
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}
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}
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callback.onResult(list, firstLoadPosition, totalCount);
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}
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@Override
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public void loadRange(@NonNull LoadRangeParams params,
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@NonNull LoadRangeCallback<T> callback) {
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callback.onResult(loadRange(params.startPosition, params.loadSize));
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}
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/**
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* Return the rows from startPos to startPos + loadCount
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*
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* @hide
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*/
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@SuppressWarnings("deprecation")
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@NonNull
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public List<T> loadRange(int startPosition, int loadCount) {
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final RoomSQLiteQuery sqLiteQuery = getSQLiteQuery(startPosition, loadCount);
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if (mInTransaction) {
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mDb.beginTransaction();
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Cursor cursor = null;
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//noinspection TryFinallyCanBeTryWithResources
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try {
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cursor = mDb.query(sqLiteQuery);
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List<T> rows = convertRows(cursor);
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mDb.setTransactionSuccessful();
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return rows;
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} finally {
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if (cursor != null) {
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cursor.close();
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}
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mDb.endTransaction();
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sqLiteQuery.release();
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}
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} else {
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Cursor cursor = mDb.query(sqLiteQuery);
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//noinspection TryFinallyCanBeTryWithResources
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try {
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return convertRows(cursor);
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} finally {
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cursor.close();
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sqLiteQuery.release();
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}
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}
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}
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private RoomSQLiteQuery getSQLiteQuery(int startPosition, int loadCount) {
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final RoomSQLiteQuery sqLiteQuery = RoomSQLiteQuery.acquire(mLimitOffsetQuery,
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mSourceQuery.getArgCount() + 2);
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sqLiteQuery.copyArgumentsFrom(mSourceQuery);
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sqLiteQuery.bindLong(sqLiteQuery.getArgCount() - 1, loadCount);
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sqLiteQuery.bindLong(sqLiteQuery.getArgCount(), startPosition);
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return sqLiteQuery;
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}
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}
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