Added comments & example methods for using Schema.SObjectField & overloaded methods (#2)

* Added comments to QueryGenerator about the design & implementation
* Cleaned up some    w h  it e   s p    a c e
* Added methods that use a Schema.SObjectField to indicate a code dependency while still using strings
* Add some overloaded & related methods to demonstrate the recommended implementation

Author: jongpie

src/classes/LeadQueryRepository.cls

@@ -3,23 +3,47 @@ public class LeadQueryRepository {
     // Each SObject should have its own repository class that contains methods for commonly used queries
     // Each method can use a different field set to generate the query fields,
     // or you can use 1 field set for all methods - tweak the code to fit your use case
+
+    // One of the most common use cases is querying for a record or list of records by ID(s)
+    // The simplest way is to have some overloaded methods with self-descriptive names
+    // The methods then use your desired field set to generate & execute the query
     public static Lead getLeadById(Id leadId) {
+        return getLeadsById(new Set<Id>{leadId})[0];
+    }
+
+    public static List<Lead> getLeadsById(List<Lead> leadList) {
+        return getLeadsById(new Map<Id, Lead>(leadList).keySet());
+    }
+
+    public static List<Lead> getLeadsById(List<Id> leadIdSet) {
+        return getLeadsById(new Set<Id>(leadIdSet));
+    }
+
+    public static List<Lead> getLeadsById(Map<Id, Lead> leadMap) {
+        return getLeadsById(leadMap.keySet());
+    }
+
+    public static List<Lead> getLeadsById(Set<Id> leadIdSet) {
         // Created a string for your where clause
-        String whereClause = 'WHERE Id = :leadId';
+        String whereClause = 'WHERE ' +  Schema.Lead.Id + ' IN :leadIdSet';
         // Created a new instance of QueryGenerator, using a field set and your where clause
         String query = new QueryGenerator(SObjectType.Lead.FieldSets.MyFieldSet).buildQuery(whereClause);
 
         // Database.query returns generic SObjects, so cast it to the desired SObject type & return it
-        return (Lead)Database.query(query);
+        return (List<Lead>)Database.query(query);
     }
 
+    // Another common use case is to query for status (or list of statuses) or similar field (like opportunity stage)
+    // These methods can all be placed into the same query repository class, or you could further break things down
+    // into multiple classes for the same SObjectType. Adapt to your use cases, but keep it simple
     public static List<Lead> getLeadsByStatus(String status) {
-        // Created a string for your where clause
-        String whereClause = 'WHERE Status = :status';
-        // Created a new instance of QueryGenerator, using a field set and your where clause
+        return getLeadsByStatuses(new List<String>{status});
+    }
+
+    public static List<Lead> getLeadsByStatuses(List<String> statuses) {
+        String whereClause = 'WHERE ' + Schema.Lead.Status + ' IN :statuses';
         String query = new QueryGenerator(SObjectType.Lead.FieldSets.MyFieldSet).buildQuery(whereClause);
 
-        // Database.query returns generic SObjects, so cast it to the desired SObject type & return it
         return (List<Lead>)Database.query(query);
     }
 

src/classes/LeadQueryRepositoryTest.cls

@@ -0,0 +1,96 @@
+@isTest
+private class LeadQueryRepositoryTest {
+
+    @testSetup
+    static void setup() {
+        List<Lead> leadList = new List<Lead>();
+        for(Integer i = 0; i < 5; i++) {
+            Lead lead = new Lead(
+                Company  = 'My Test Company',
+                LastName = 'Gillespie'
+            );
+            leadList.add(lead);
+        }
+        insert leadList;
+    }
+
+    @isTest
+    static void getLeadById_Test() {
+        Lead expectedLead = [SELECT Id FROM Lead LIMIT 1];
+
+        Test.startTest();
+
+        Lead returnedLead = LeadQueryRepository.getLeadById(expectedLead.Id);
+
+        Test.stopTest();
+    }
+
+    @isTest
+    static void getLeadsById_WHEN_parameterIsAListOfIds() {
+        List<Lead> expectedLeads    = [SELECT Id FROM Lead];
+        List<Id> expectedLeadIdList = new List<Id>(new Map<Id, Lead>(expectedLeads).keySet());
+
+        Test.startTest();
+
+        List<Lead> returnedLeadList = LeadQueryRepository.getLeadsById(expectedLeadIdList);
+
+        Test.stopTest();
+    }
+
+    @isTest
+    static void getLeadsById_WHEN_parameterIsAListOfRecords() {
+        List<Lead> expectedLeadList = [SELECT Id FROM Lead];
+
+        Test.startTest();
+
+        List<Lead> returnedLeads = LeadQueryRepository.getLeadsById(expectedLeadList);
+
+        Test.stopTest();
+    }
+
+    @isTest
+    static void getLeadsById_WHEN_parameterIsAMap() {
+        Map<Id, Lead> expectedLeadMap = new Map<Id, Lead>([SELECT Id FROM Lead]);
+
+        Test.startTest();
+
+        List<Lead> returnedLeads = LeadQueryRepository.getLeadsById(expectedLeadMap);
+
+        Test.stopTest();
+    }
+
+    @isTest
+    static void getLeadsById_WHEN_parameterIsASetOfIds() {
+        Set<Id> expectedLeadIdSet = new Map<Id, Lead>([SELECT Id FROM Lead]).keySet();
+
+        Test.startTest();
+
+        List<Lead> returnedLeadList = LeadQueryRepository.getLeadsById(expectedLeadIdSet);
+
+        Test.stopTest();
+    }
+
+    @isTest
+    static void getLeadsByStatus() {
+        Lead lead = [SELECT Id, Status FROM Lead LIMIT 1];
+
+        Test.startTest();
+
+        List<Lead> returnedLeadList = LeadQueryRepository.getLeadsByStatus(lead.Status);
+
+        Test.stopTest();
+    }
+
+    @isTest
+    static void getLeadsByStatuses() {
+        Lead lead = [SELECT Id, Status FROM Lead LIMIT 1];
+        List<String> leadStatusList = new List<String>{lead.Status};
+
+        Test.startTest();
+
+        List<Lead> returnedLeadList = LeadQueryRepository.getLeadsByStatuses(leadStatusList);
+
+        Test.stopTest();
+    }
+
+}

src/classes/LeadQueryRepositoryTest.cls-meta.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
+    <apiVersion>38.0</apiVersion>
+    <status>Active</status>
+</ApexClass>

src/classes/QueryGenerator.cls

@@ -1,14 +1,20 @@
 public class QueryGenerator {
 
+    // Each query repository class will have one or more methods that handle generating a query
+    // This class handles taking a fieldSet and an optional string for a WHERE statement
+    // Everything is parsed and a query string is returned to the originating query repository class
+    // The query repository should handle executing the query so that any relevant variables are in scope
+    // Finally, it should cast the SObjects to the appropriate SObjectType
+
     private Schema.FieldSet fieldSet;
     private SObjectType sobjectType;
     private Set<String> queryFields;
 
     public QueryGenerator(Schema.FieldSet fieldSet) {
-        this.fieldSet      = fieldSet;
+        this.fieldSet    = fieldSet;
 
-        this.sobjectType   = fieldSet.getSObjectType();
-        this.queryFields   = new Set<String>{'Id'}; // Always add the ID field, just in case it's not in the field set
+        this.sobjectType = fieldSet.getSObjectType();
+        this.queryFields = new Set<String>{'Id'}; // Always add the ID field, just in case it's not in the field set
 
         this.parseFieldSetMembers();
     }