Polymorphic fields

force-app/main/default/classes/Q.cls

@@ -10,6 +10,7 @@ public class Q {
 	private Integer numberOfRowsToSkip;
 
 	private Set<String> fieldList = new Set<String>();
+	private List<QTypeOf.QTypeOfBuilder> typeOfList = new List<QTypeOf.QTypeOfBuilder>();
 	private List<QOrder> orders = new List<QOrder>();
 	private List<QICondition> conditions = new List<QICondition>();
 	private List<Q> subQueries = new List<Q>();
@@ -67,6 +68,14 @@ public class Q {
 		return this;
 	}
 
+	/**
+     * Instantiate a QTypeOf object for polymorphic relationship query support
+     */
+    public static QTypeOf.QTypeOfBuilder typeOf(String fieldName) {
+        QTypeOf.QTypeOfBuilder typeOf = new QTypeOf.QTypeOfBuilder(fieldName);
+        return typeOf;
+	}
+
 	/**
 	 * Add fields to the SELECT statement from Set of Strings
 	 */
@@ -77,6 +86,14 @@ public class Q {
 		return this;
 	}
 
+	/**
+     * Add fields to the SELECT statement with TYPEOF logic
+     */
+    public Q selectFields(QTypeOf.QTypeOfBuilder typeOf) {
+        this.typeOfList.add(typeOf);
+        return this;
+    }
+
 	/**
 	 * Add a LIMIT statement
 	 */
@@ -117,6 +134,10 @@ public class Q {
 			this.fieldList.add('(' + qb.build() + ')');
 		}
 
+		for (QTypeOf.QTypeOfBuilder typeOfVal : this.typeOfList) {
+            this.fieldList.add(typeOfVal.build());
+        }
+
 		if (!this.fieldList.isEmpty()) {
 			return 'SELECT ' + String.join(new List<String>(this.fieldList), ', ');
 		} else {

force-app/main/default/classes/QAndGroup.cls-meta.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
-    <apiVersion>47.0</apiVersion>
+    <apiVersion>48.0</apiVersion>
     <status>Active</status>
 </ApexClass>

force-app/main/default/classes/QConditionGroup.cls-meta.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
-    <apiVersion>47.0</apiVersion>
+    <apiVersion>48.0</apiVersion>
     <status>Active</status>
 </ApexClass>

force-app/main/default/classes/QICondition.cls-meta.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
-    <apiVersion>47.0</apiVersion>
+    <apiVersion>48.0</apiVersion>
     <status>Active</status>
 </ApexClass>

force-app/main/default/classes/QOrGroup.cls-meta.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
-    <apiVersion>47.0</apiVersion>
+    <apiVersion>48.0</apiVersion>
     <status>Active</status>
 </ApexClass>

force-app/main/default/classes/QTest.cls

@@ -114,6 +114,29 @@ private class QTest {
 		Database.query(query);
 	}
 
+	@isTest
+	static void testTypeOf() {
+		String query =
+			new Q(Event.SObjectType)
+				.selectFields(Q.typeOf('What')
+					.when('Account').then(new Set<String> {'Phone', 'NumberOfEmployees'})   
+					.when('Opportunity').then(new Set<String> {'Amount', 'CloseDate'})                 
+					.otherwise(new Set<String> {'Name', 'Email'})
+				)
+				.build();
+
+		String expected = 'SELECT ' + 
+							'TYPEOF What ' +
+							'WHEN Account THEN Phone,NumberOfEmployees ' +
+							'WHEN Opportunity THEN Amount,CloseDate ' +
+							'ELSE Name,Email ' +
+							'END ' +
+						'FROM Event';
+
+		System.assertEquals(expected, query, 'It should output a query with a TYPEOF');
+		Database.query(query);
+	}
+
 	@isTest
     static void testOrGroup() {
         String query =

force-app/main/default/classes/QTypeOf.cls

@@ -0,0 +1,57 @@
+/**
+* QTypeOf is a class used to build TYPEOF statement in the SELECT statement
+* @author  Fred Hays
+* @since   2020-04-29
+*/
+
+public class QTypeOf {
+
+    // interfaces used to enforce valid method chaining order
+    public interface IWhen {
+        IThen when(String objectName);
+        QTypeOfBuilder otherwise(Set<String> fieldNames);
+    }
+
+    public interface IThen {
+        IWhen then(Set<String> fieldSet);
+    }
+
+    public class QTypeOfBuilder implements IWhen, IThen {
+
+        private String whenFieldName;
+        private Set<String> elseFieldNames = new Set<String>();
+        private Map<String, Set<String>> whenItems = new Map<String, Set<String>>();
+        private String currentObjectName;
+
+        public QTypeOfBuilder(String whenFieldName) {
+            this.whenFieldName = whenFieldName;
+        }
+
+        public IThen when(String objectName) {
+            this.currentObjectName = objectName;
+            return this;
+        }
+
+        public IWhen then(Set<String> fieldSet) {
+            this.whenItems.put(this.currentObjectName, fieldSet);
+            return this;
+        }
+
+        public QTypeOfBuilder otherwise(Set<String> elseFieldNames) {
+            this.elseFieldNames = elseFieldNames;
+            return this;
+        }
+
+        public String build() {
+            String val = 'TYPEOF ' + this.whenFieldName + ' ';
+            for (String objectName : this.whenItems.keySet()) {
+                val += 'WHEN ' + objectName + ' THEN ' + String.join(new List<String>(this.whenItems.get(objectName)), ',') + ' ';
+            }
+            if (!this.elseFieldNames.isEmpty()) {
+                val += 'ELSE ' + String.join(new List<String>(this.elseFieldNames), ',') + ' ';
+            }
+            val += 'END';
+            return val;
+        }
+    }
+}

force-app/main/default/classes/QTypeOf.cls-meta.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
+    <apiVersion>48.0</apiVersion>
+    <status>Active</status>
+</ApexClass>