Fix bug for https://github.com/LitePalFramework/LitePal/issues/606.

core/src/main/java/org/litepal/FluentQuery.java

@@ -16,12 +16,15 @@
 
 package org.litepal;
 
+import android.text.TextUtils;
+
 import org.litepal.crud.LitePalSupport;
 import org.litepal.crud.QueryHandler;
 import org.litepal.crud.async.AverageExecutor;
 import org.litepal.crud.async.CountExecutor;
 import org.litepal.crud.async.FindExecutor;
 import org.litepal.crud.async.FindMultiExecutor;
+import org.litepal.exceptions.LitePalSupportException;
 import org.litepal.tablemanager.Connector;
 import org.litepal.util.BaseUtility;
 import org.litepal.util.DBUtility;
@@ -313,8 +316,14 @@ public class FluentQuery {
      */
     public <T> T findFirst(Class<T> modelClass, boolean isEager) {
         synchronized (LitePalSupport.class) {
+        	String limitTemp = mLimit;
+        	if (!"0".equals(mLimit)) { // If mLimit not equals to 0, set mLimit to 1 to find the first record.
+        		mLimit = "1";
+			}
             List<T> list = find(modelClass, isEager);
+        	mLimit = limitTemp; // Don't forget to change it back after finding operation.
             if (list.size() > 0) {
+				if (list.size() != 1) throw new LitePalSupportException("Found multiple records while only one record should be found at most.");
                 return list.get(0);
             }
             return null;
@@ -399,7 +408,29 @@ public class FluentQuery {
      */
     public <T> T findLast(Class<T> modelClass, boolean isEager) {
         synchronized (LitePalSupport.class) {
+			String orderByTemp = mOrderBy;
+			String limitTemp = mLimit;
+        	if (TextUtils.isEmpty(mOffset) && TextUtils.isEmpty(mLimit)) { // If mOffset or mLimit is specified, we can't use the strategy in this block to speed up finding.
+				if (TextUtils.isEmpty(mOrderBy)) {
+					// If mOrderBy is null, we can use id desc order, then the first record will be the record value where want to find.
+					mOrderBy = "id desc";
+				} else {
+					// If mOrderBy is not null, check if it ends with desc.
+					if (mOrderBy.endsWith(" desc")) {
+						// If mOrderBy ends with desc, then the last record of desc order will be the first record of asc order, so we remove the desc.
+						mOrderBy = mOrderBy.replace(" desc", "");
+					} else {
+						// If mOrderBy not ends with desc, then the last record of asc order will be the first record of desc order, so we add the desc.
+						mOrderBy += " desc";
+					}
+				}
+				if (!"0".equals(mLimit)) {
+					mLimit = "1";
+				}
+			}
             List<T> list = find(modelClass, isEager);
+        	mOrderBy = orderByTemp;
+        	mLimit = limitTemp;
             int size = list.size();
             if (size > 0) {
                 return list.get(size - 1);

sample/src/androidTest/java/com/litepaltest/test/crud/query/QueryClusterTest.java

@@ -289,6 +289,23 @@ public class QueryClusterTest extends LitePalTestCase {
                 assertEquals(lastBook.getId(), b.getId());
             }
 		}
+
+		Book first1 = LitePal.findFirst(Book.class);
+		Book first2 = LitePal.select("id").findFirst(Book.class);
+		assertEquals(first1.getId(), first2.getId());
+
+		Book last1 = LitePal.findLast(Book.class);
+		Book last2 = LitePal.select("id").findLast(Book.class);
+		assertEquals(last1.getId(), last2.getId());
+
+		List<Book> firstTwoBooks = LitePal.where("id=? or id=? or id=?", String.valueOf(ids[0]), String.valueOf(ids[1]),
+				String.valueOf(ids[2])).order("id").limit(2).find(Book.class);
+		firstBook = LitePal.where("id=? or id=? or id=?", String.valueOf(ids[0]), String.valueOf(ids[1]),
+				String.valueOf(ids[2])).order("id").limit(2).findFirst(Book.class);
+		lastBook = LitePal.where("id=? or id=? or id=?", String.valueOf(ids[0]), String.valueOf(ids[1]),
+				String.valueOf(ids[2])).order("id").limit(2).findLast(Book.class);
+		assertEquals(firstTwoBooks.get(0).getId(), firstBook.getId());
+		assertEquals(firstTwoBooks.get(1).getId(), lastBook.getId());
 	}
 
 }