diff --git a/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/base/RuleCollections.java b/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/base/RuleCollections.java
index 1f3801c..e13da67 100644
--- a/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/base/RuleCollections.java
+++ b/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/base/RuleCollections.java
@@ -35,6 +35,7 @@
 import edu.uci.ics.asterix.optimizer.rules.IntroduceRapidFrameFlushProjectRule;
 import edu.uci.ics.asterix.optimizer.rules.IntroduceSecondaryIndexInsertDeleteRule;
 import edu.uci.ics.asterix.optimizer.rules.IntroduceStaticTypeCastForInsertRule;
+import edu.uci.ics.asterix.optimizer.rules.IntroduceUnnestForCollectionToSequenceRule;
 import edu.uci.ics.asterix.optimizer.rules.LoadRecordFieldsRule;
 import edu.uci.ics.asterix.optimizer.rules.NestGroupByRule;
 import edu.uci.ics.asterix.optimizer.rules.NestedSubplanToJoinRule;
@@ -110,6 +111,7 @@
 
     public final static List<IAlgebraicRewriteRule> buildNormalizationRuleCollection() {
         List<IAlgebraicRewriteRule> normalization = new LinkedList<IAlgebraicRewriteRule>();
+        normalization.add(new IntroduceUnnestForCollectionToSequenceRule());
         normalization.add(new EliminateSubplanRule());
         normalization.add(new EnforceOrderByAfterSubplan());
         normalization.add(new PushAggFuncIntoStandaloneAggregateRule());
diff --git a/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/rules/IntroduceUnnestForCollectionToSequenceRule.java b/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/rules/IntroduceUnnestForCollectionToSequenceRule.java
new file mode 100644
index 0000000..984f4dd
--- /dev/null
+++ b/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/rules/IntroduceUnnestForCollectionToSequenceRule.java
@@ -0,0 +1,94 @@
+/*
+ * Copyright 2009-2013 by The Regents of the University of California
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * you may obtain a copy of the License from
+ * 
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package edu.uci.ics.asterix.optimizer.rules;
+
+import java.util.List;
+
+import org.apache.commons.lang3.mutable.Mutable;
+import org.apache.commons.lang3.mutable.MutableObject;
+
+import edu.uci.ics.asterix.aql.util.FunctionUtils;
+import edu.uci.ics.asterix.om.functions.AsterixBuiltinFunctions;
+import edu.uci.ics.asterix.om.types.IAType;
+import edu.uci.ics.hyracks.algebricks.common.exceptions.AlgebricksException;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.ILogicalExpression;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.ILogicalOperator;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.IOptimizationContext;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.LogicalExpressionTag;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.LogicalOperatorTag;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.LogicalVariable;
+import edu.uci.ics.hyracks.algebricks.core.algebra.expressions.AbstractFunctionCallExpression;
+import edu.uci.ics.hyracks.algebricks.core.algebra.expressions.IVariableTypeEnvironment;
+import edu.uci.ics.hyracks.algebricks.core.algebra.expressions.UnnestingFunctionCallExpression;
+import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
+import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.AssignOperator;
+import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.UnnestOperator;
+import edu.uci.ics.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
+
+/**
+ * This rule introduces a unnest operator for the collection-to-sequence function (if the input to the function is a collection).
+ * 
+ * @author yingyib
+ */
+public class IntroduceUnnestForCollectionToSequenceRule implements IAlgebraicRewriteRule {
+
+    @Override
+    public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context) throws AlgebricksException {
+        return false;
+    }
+
+    @Override
+    public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
+            throws AlgebricksException {
+        AbstractLogicalOperator op = (AbstractLogicalOperator) opRef.getValue();
+        if (op.getOperatorTag() != LogicalOperatorTag.ASSIGN) {
+            return false;
+        }
+        AssignOperator assign = (AssignOperator) op;
+        List<Mutable<ILogicalExpression>> exprs = assign.getExpressions();
+        if (exprs.size() != 1) {
+            return false;
+        }
+        ILogicalExpression expr = exprs.get(0).getValue();
+        if (expr.getExpressionTag() != LogicalExpressionTag.FUNCTION_CALL) {
+            return false;
+        }
+        AbstractFunctionCallExpression func = (AbstractFunctionCallExpression) expr;
+        if (func.getFunctionIdentifier() != AsterixBuiltinFunctions.COLLECTION_TO_SEQUENCE) {
+            return false;
+        }
+
+        IVariableTypeEnvironment env = assign.computeInputTypeEnvironment(context);
+        ILogicalExpression argExpr = func.getArguments().get(0).getValue();
+        IAType outerExprType = (IAType) env.getType(expr);
+        IAType innerExprType = (IAType) env.getType(argExpr);
+        if (outerExprType.equals(innerExprType)) {
+            /** nothing is changed with the collection-to-sequence function, remove the collection-sequence function call */
+            assign.getExpressions().set(0, new MutableObject<ILogicalExpression>(argExpr));
+            return true;
+        }
+        /** change the assign operator to an unnest operator */
+        LogicalVariable var = assign.getVariables().get(0);
+        @SuppressWarnings("unchecked")
+        UnnestOperator unnest = new UnnestOperator(var, new MutableObject<ILogicalExpression>(
+                new UnnestingFunctionCallExpression(
+                        FunctionUtils.getFunctionInfo(AsterixBuiltinFunctions.SCAN_COLLECTION),
+                        new MutableObject<ILogicalExpression>(argExpr))));
+        unnest.getInputs().addAll(assign.getInputs());
+        opRef.setValue(unnest);
+        context.computeAndSetTypeEnvironmentForOperator(unnest);
+        return true;
+    }
+}
diff --git a/asterix-algebra/src/main/java/edu/uci/ics/asterix/translator/AqlExpressionToPlanTranslator.java b/asterix-algebra/src/main/java/edu/uci/ics/asterix/translator/AqlExpressionToPlanTranslator.java
index a2545ff..fc4bb03d7 100644
--- a/asterix-algebra/src/main/java/edu/uci/ics/asterix/translator/AqlExpressionToPlanTranslator.java
+++ b/asterix-algebra/src/main/java/edu/uci/ics/asterix/translator/AqlExpressionToPlanTranslator.java
@@ -187,13 +187,13 @@
         ILogicalOperator topOp = p.first;
         ProjectOperator project = (ProjectOperator) topOp;
         LogicalVariable resVar = project.getVariables().get(0);
+
         if (outputDatasetName == null) {
             FileSplit outputFileSplit = metadataProvider.getOutputFile();
             if (outputFileSplit == null) {
                 outputFileSplit = getDefaultOutputFileLocation();
             }
             metadataProvider.setOutputFile(outputFileSplit);
-            String resultNodeName = outputFileSplit.getNodeName();
 
             List<Mutable<ILogicalExpression>> writeExprList = new ArrayList<Mutable<ILogicalExpression>>(1);
             writeExprList.add(new MutableObject<ILogicalExpression>(new VariableReferenceExpression(resVar)));
@@ -202,6 +202,20 @@
             topOp = new DistributeResultOperator(writeExprList, sink);
             topOp.getInputs().add(new MutableObject<ILogicalOperator>(project));
         } else {
+            /** add the collection-to-sequence right before the final project, because dataset only accept non-collection records */
+            LogicalVariable seqVar = context.newVar();
+            @SuppressWarnings("unchecked")
+            /** This assign adds a marker function collection-to-sequence: if the input is a singleton collection, unnest it; otherwise do nothing. */
+            AssignOperator assignCollectionToSequence = new AssignOperator(seqVar,
+                    new MutableObject<ILogicalExpression>(
+                            new ScalarFunctionCallExpression(AsterixBuiltinFunctions
+                                    .getAsterixFunctionInfo(AsterixBuiltinFunctions.COLLECTION_TO_SEQUENCE),
+                                    new MutableObject<ILogicalExpression>(new VariableReferenceExpression(resVar)))));
+            assignCollectionToSequence.getInputs().add(
+                    new MutableObject<ILogicalOperator>(project.getInputs().get(0).getValue()));
+            project.getInputs().get(0).setValue(assignCollectionToSequence);
+            project.getVariables().set(0, seqVar);
+            resVar = seqVar;
 
             AqlDataSource targetDatasource = validateDatasetInfo(metadataProvider, stmt.getDataverseName(),
                     stmt.getDatasetName());
@@ -225,7 +239,6 @@
             }
             AssignOperator assign = new AssignOperator(vars, exprs);
             assign.getInputs().add(new MutableObject<ILogicalOperator>(project));
-
             Mutable<ILogicalExpression> varRef = new MutableObject<ILogicalExpression>(new VariableReferenceExpression(
                     resVar));
             ILogicalOperator leafOperator = null;
diff --git a/asterix-app/src/test/resources/optimizerts/results/scan-delete-all.plan b/asterix-app/src/test/resources/optimizerts/results/scan-delete-all.plan
index e969e5d..cba987c 100644
--- a/asterix-app/src/test/resources/optimizerts/results/scan-delete-all.plan
+++ b/asterix-app/src/test/resources/optimizerts/results/scan-delete-all.plan
@@ -3,8 +3,8 @@
     -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
       -- INSERT_DELETE  |PARTITIONED|
         -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-          -- STABLE_SORT [$$19(ASC)]  |PARTITIONED|
-            -- HASH_PARTITION_EXCHANGE [$$19]  |PARTITIONED|
+          -- STABLE_SORT [$$20(ASC)]  |PARTITIONED|
+            -- HASH_PARTITION_EXCHANGE [$$20]  |PARTITIONED|
               -- ASSIGN  |PARTITIONED|
                 -- STREAM_PROJECT  |PARTITIONED|
                   -- ASSIGN  |PARTITIONED|
diff --git a/asterix-app/src/test/resources/optimizerts/results/scan-delete-rtree-secondary-index.plan b/asterix-app/src/test/resources/optimizerts/results/scan-delete-rtree-secondary-index.plan
index 4f0d931..e1852af 100644
--- a/asterix-app/src/test/resources/optimizerts/results/scan-delete-rtree-secondary-index.plan
+++ b/asterix-app/src/test/resources/optimizerts/results/scan-delete-rtree-secondary-index.plan
@@ -10,8 +10,8 @@
                   -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
                     -- INSERT_DELETE  |PARTITIONED|
                       -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                        -- STABLE_SORT [$$14(ASC)]  |PARTITIONED|
-                          -- HASH_PARTITION_EXCHANGE [$$14]  |PARTITIONED|
+                        -- STABLE_SORT [$$15(ASC)]  |PARTITIONED|
+                          -- HASH_PARTITION_EXCHANGE [$$15]  |PARTITIONED|
                             -- ASSIGN  |PARTITIONED|
                               -- STREAM_PROJECT  |PARTITIONED|
                                 -- ASSIGN  |PARTITIONED|
@@ -20,4 +20,4 @@
                                       -- BTREE_SEARCH  |PARTITIONED|
                                         -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
                                           -- ASSIGN  |PARTITIONED|
-                                            -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
\ No newline at end of file
+                                            -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
diff --git a/asterix-app/src/test/resources/optimizerts/results/scan-delete.plan b/asterix-app/src/test/resources/optimizerts/results/scan-delete.plan
index 0608f69..a5265c8 100644
--- a/asterix-app/src/test/resources/optimizerts/results/scan-delete.plan
+++ b/asterix-app/src/test/resources/optimizerts/results/scan-delete.plan
@@ -3,8 +3,8 @@
     -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
       -- INSERT_DELETE  |PARTITIONED|
         -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-          -- STABLE_SORT [$$21(ASC)]  |PARTITIONED|
-            -- HASH_PARTITION_EXCHANGE [$$21]  |PARTITIONED|
+          -- STABLE_SORT [$$22(ASC)]  |PARTITIONED|
+            -- HASH_PARTITION_EXCHANGE [$$22]  |PARTITIONED|
               -- ASSIGN  |PARTITIONED|
                 -- STREAM_PROJECT  |PARTITIONED|
                   -- ASSIGN  |PARTITIONED|
diff --git a/asterix-app/src/test/resources/optimizerts/results/scan-insert-secondary-index.plan b/asterix-app/src/test/resources/optimizerts/results/scan-insert-secondary-index.plan
index 1458c66..8057666 100644
--- a/asterix-app/src/test/resources/optimizerts/results/scan-insert-secondary-index.plan
+++ b/asterix-app/src/test/resources/optimizerts/results/scan-insert-secondary-index.plan
@@ -13,8 +13,8 @@
                         -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
                           -- INSERT_DELETE  |PARTITIONED|
                             -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                              -- STABLE_SORT [$$6(ASC)]  |PARTITIONED|
-                                -- HASH_PARTITION_EXCHANGE [$$6]  |PARTITIONED|
+                              -- STABLE_SORT [$$7(ASC)]  |PARTITIONED|
+                                -- HASH_PARTITION_EXCHANGE [$$7]  |PARTITIONED|
                                   -- ASSIGN  |PARTITIONED|
                                     -- STREAM_PROJECT  |PARTITIONED|
                                       -- ASSIGN  |PARTITIONED|
diff --git a/asterix-app/src/test/resources/optimizerts/results/scan-insert.plan b/asterix-app/src/test/resources/optimizerts/results/scan-insert.plan
index 0b756d9..51d3060 100644
--- a/asterix-app/src/test/resources/optimizerts/results/scan-insert.plan
+++ b/asterix-app/src/test/resources/optimizerts/results/scan-insert.plan
@@ -3,8 +3,8 @@
     -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
       -- INSERT_DELETE  |PARTITIONED|
         -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-          -- STABLE_SORT [$$6(ASC)]  |PARTITIONED|
-            -- HASH_PARTITION_EXCHANGE [$$6]  |PARTITIONED|
+          -- STABLE_SORT [$$7(ASC)]  |PARTITIONED|
+            -- HASH_PARTITION_EXCHANGE [$$7]  |PARTITIONED|
               -- ASSIGN  |PARTITIONED|
                 -- STREAM_PROJECT  |PARTITIONED|
                   -- ASSIGN  |PARTITIONED|
diff --git a/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue244/query-issue244.1.ddl.aql b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue244/query-issue244.1.ddl.aql
new file mode 100644
index 0000000..45667b1
--- /dev/null
+++ b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue244/query-issue244.1.ddl.aql
@@ -0,0 +1,25 @@
+/*
+ * Description  : This test case is to verify the fix for issue244
+ 				: https://code.google.com/p/asterixdb/issues/detail?id=244
+ * Expected Res : Success
+ * Date         : 31th May 2013
+ */
+
+
+drop dataverse test if exists;
+create dataverse test;
+
+use dataverse test;
+
+create type TypeA as open {
+    id : int32,
+    name : string
+}
+
+create dataset t1(TypeA) primary key id;
+
+create dataset t2(TypeA) primary key id;
+
+create function f1(){
+for $m in dataset('t1') return $m
+};
diff --git a/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue244/query-issue244.2.update.aql b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue244/query-issue244.2.update.aql
new file mode 100644
index 0000000..8f7d86a
--- /dev/null
+++ b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue244/query-issue244.2.update.aql
@@ -0,0 +1,16 @@
+/*
+ * Description  : This test case is to verify the fix for issue244
+ 				: https://code.google.com/p/asterixdb/issues/detail?id=244
+ * Expected Res : Success
+ * Date         : 31th May 2013
+ */
+
+use dataverse test;
+ 
+insert into dataset t1({"id":21,"name":"John"});
+insert into dataset t1({"id":34,"name":"Bill"});
+insert into dataset t1({"id":41,"name":"Joy"});
+insert into dataset t1({"id":16,"name":"Sam"});
+insert into dataset t1({"id":67,"name":"Ravi"});
+
+insert into dataset t2(f1());
\ No newline at end of file
diff --git a/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue244/query-issue244.3.query.aql b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue244/query-issue244.3.query.aql
new file mode 100644
index 0000000..41b3211
--- /dev/null
+++ b/asterix-app/src/test/resources/runtimets/queries/user-defined-functions/query-issue244/query-issue244.3.query.aql
@@ -0,0 +1,11 @@
+/*
+ * Description  : This test case is to verify the fix for issue244
+ 				: https://code.google.com/p/asterixdb/issues/detail?id=244
+ * Expected Res : Success
+ * Date         : 31th May 2013
+ */
+ 
+use dataverse test;
+ 
+for $l in dataset('t2')
+return $l;
diff --git a/asterix-app/src/test/resources/runtimets/results/user-defined-functions/query-issue244/query-issue244.1.adm b/asterix-app/src/test/resources/runtimets/results/user-defined-functions/query-issue244/query-issue244.1.adm
new file mode 100644
index 0000000..79d009c
--- /dev/null
+++ b/asterix-app/src/test/resources/runtimets/results/user-defined-functions/query-issue244/query-issue244.1.adm
@@ -0,0 +1,5 @@
+{ "id": 21, "name": "John" }
+{ "id": 34, "name": "Bill" }
+{ "id": 41, "name": "Joy" }
+{ "id": 67, "name": "Ravi" }
+{ "id": 16, "name": "Sam" }
diff --git a/asterix-app/src/test/resources/runtimets/testsuite.xml b/asterix-app/src/test/resources/runtimets/testsuite.xml
index 52d5dab..c7260184 100644
--- a/asterix-app/src/test/resources/runtimets/testsuite.xml
+++ b/asterix-app/src/test/resources/runtimets/testsuite.xml
@@ -4177,6 +4177,11 @@
         <output-dir compare="Text">issue289_query</output-dir>
       </compilation-unit>
     </test-case>
+     <test-case FilePath="user-defined-functions">
+      <compilation-unit name="query-issue244">
+        <output-dir compare="Text">query-issue244</output-dir>
+      </compilation-unit>
+    </test-case>
   </test-group>
   <test-group name="hints">
     <test-case FilePath="hints">
diff --git a/asterix-common/src/test/java/edu/uci/ics/asterix/test/aql/TestsUtils.java b/asterix-common/src/test/java/edu/uci/ics/asterix/test/aql/TestsUtils.java
index ac8a3bd..d13dd2e 100644
--- a/asterix-common/src/test/java/edu/uci/ics/asterix/test/aql/TestsUtils.java
+++ b/asterix-common/src/test/java/edu/uci/ics/asterix/test/aql/TestsUtils.java
@@ -236,7 +236,7 @@
             GlobalConfig.ASTERIX_LOGGER.log(Level.SEVERE, "Method failed: " + method.getStatusLine());
             String[] errors = handleError(method);
             GlobalConfig.ASTERIX_LOGGER.log(Level.SEVERE, errors[2]);
-            throw new Exception("DDL operation failed: " + errors[0]);
+            throw new Exception("DML operation failed: " + errors[0]);
         }
     }
 
diff --git a/asterix-om/src/main/java/edu/uci/ics/asterix/om/functions/AsterixBuiltinFunctions.java b/asterix-om/src/main/java/edu/uci/ics/asterix/om/functions/AsterixBuiltinFunctions.java
index 2a732ac..f717653 100644
--- a/asterix-om/src/main/java/edu/uci/ics/asterix/om/functions/AsterixBuiltinFunctions.java
+++ b/asterix-om/src/main/java/edu/uci/ics/asterix/om/functions/AsterixBuiltinFunctions.java
@@ -31,6 +31,7 @@
 import edu.uci.ics.asterix.om.typecomputer.impl.CastListResultTypeComputer;
 import edu.uci.ics.asterix.om.typecomputer.impl.CastRecordResultTypeComputer;
 import edu.uci.ics.asterix.om.typecomputer.impl.ClosedRecordConstructorResultType;
+import edu.uci.ics.asterix.om.typecomputer.impl.CollectionToSequenceTypeComputer;
 import edu.uci.ics.asterix.om.typecomputer.impl.ConcatNonNullTypeComputer;
 import edu.uci.ics.asterix.om.typecomputer.impl.FieldAccessByIndexResultType;
 import edu.uci.ics.asterix.om.typecomputer.impl.InjectFailureTypeComputer;
@@ -561,6 +562,8 @@
 
     public static final FunctionIdentifier NOT_NULL = new FunctionIdentifier(FunctionConstants.ASTERIX_NS, "not-null",
             1);
+    public static final FunctionIdentifier COLLECTION_TO_SEQUENCE = new FunctionIdentifier(
+            FunctionConstants.ASTERIX_NS, "" + "collection-to-sequence", 1);
 
     public static IFunctionInfo getAsterixFunctionInfo(FunctionIdentifier fid) {
         IFunctionInfo finfo = registeredFunctions.get(fid);
@@ -862,6 +865,8 @@
         addFunction(INTERVAL_CONSTRUCTOR_START_FROM_DATETIME, OptionalAIntervalTypeComputer.INSTANCE);
         addFunction(INTERVAL_CONSTRUCTOR_START_FROM_TIME, OptionalAIntervalTypeComputer.INSTANCE);
 
+        addPrivateFunction(COLLECTION_TO_SEQUENCE, CollectionToSequenceTypeComputer.INSTANCE);
+
         String metadataFunctionLoaderClassName = "edu.uci.ics.asterix.metadata.functions.MetadataBuiltinFunctions";
         try {
             Class.forName(metadataFunctionLoaderClassName);
diff --git a/asterix-om/src/main/java/edu/uci/ics/asterix/om/typecomputer/impl/CollectionToSequenceTypeComputer.java b/asterix-om/src/main/java/edu/uci/ics/asterix/om/typecomputer/impl/CollectionToSequenceTypeComputer.java
new file mode 100644
index 0000000..5066d4b
--- /dev/null
+++ b/asterix-om/src/main/java/edu/uci/ics/asterix/om/typecomputer/impl/CollectionToSequenceTypeComputer.java
@@ -0,0 +1,65 @@
+/*
+ * Copyright 2009-2013 by The Regents of the University of California
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * you may obtain a copy of the License from
+ * 
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package edu.uci.ics.asterix.om.typecomputer.impl;
+
+import edu.uci.ics.asterix.om.typecomputer.base.IResultTypeComputer;
+import edu.uci.ics.asterix.om.types.ATypeTag;
+import edu.uci.ics.asterix.om.types.AbstractCollectionType;
+import edu.uci.ics.asterix.om.types.IAType;
+import edu.uci.ics.asterix.om.types.TypeHelper;
+import edu.uci.ics.hyracks.algebricks.common.exceptions.AlgebricksException;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.ILogicalExpression;
+import edu.uci.ics.hyracks.algebricks.core.algebra.expressions.AbstractFunctionCallExpression;
+import edu.uci.ics.hyracks.algebricks.core.algebra.expressions.IVariableTypeEnvironment;
+import edu.uci.ics.hyracks.algebricks.core.algebra.metadata.IMetadataProvider;
+
+/**
+ * This function is to make a sequence of records and a singleton collection of records
+ * present in a uniformed manner.
+ * 
+ * @author yingyib
+ */
+public class CollectionToSequenceTypeComputer implements IResultTypeComputer {
+
+    public static final CollectionToSequenceTypeComputer INSTANCE = new CollectionToSequenceTypeComputer();
+
+    @Override
+    public IAType computeType(ILogicalExpression expression, IVariableTypeEnvironment env,
+            IMetadataProvider<?, ?> metadataProvider) throws AlgebricksException {
+        AbstractFunctionCallExpression func = (AbstractFunctionCallExpression) expression;
+        ILogicalExpression arg = func.getArguments().get(0).getValue();
+
+        IAType argType = (IAType) env.getType(arg);
+        if (TypeHelper.canBeNull(argType)) {
+            IAType nonOptionalType = TypeHelper.getNonOptionalType(argType);
+            if (nonOptionalType.getTypeTag() == ATypeTag.ORDEREDLIST
+                    || nonOptionalType.getTypeTag() == ATypeTag.UNORDEREDLIST) {
+                /** if the collection is null, that corresponds to an empty sequence */
+                argType = nonOptionalType;
+            }
+        }
+
+        ATypeTag argTypeTag = argType.getTypeTag();
+        if (argTypeTag == ATypeTag.ORDEREDLIST || argTypeTag == ATypeTag.UNORDEREDLIST) {
+            /** if the input is a singleton list, return it's item type if any */
+            AbstractCollectionType collectionType = (AbstractCollectionType) argType;
+            return collectionType.getItemType();
+        } else {
+            /** if the input is not a singleton list, return the original input type */
+            return argType;
+        }
+    }
+
+}