Add support for Substring SQL Expression to SQL Server

src/ServiceStack.OrmLite.SqlServer/SqlServerExpression.cs

@@ -33,5 +33,12 @@ public override string ToUpdateStatement(T item, bool excludeDefaults = false)
             return string.Format("UPDATE {0} SET {1} {2}",
                 base.DialectProvider.GetQuotedTableName(ModelDef), setFields, WhereExpression);
         }
-	}
+
+	    public override string GetSubstringSql(object quotedColumn, int startIndex, int? length = null)
+	    {
+            return length != null
+                ? string.Format("substring({0}, {1}, {2})", quotedColumn, startIndex, length.Value)
+                : string.Format("substring({0}, {1}, LEN({0}) - {1} + 1)", quotedColumn, startIndex );
+        }
+    }
 }

src/ServiceStack.OrmLite/Expressions/SqlExpression.cs

@@ -1644,26 +1644,30 @@ protected virtual object VisitColumnAccessMethod(MethodCallExpression m)
                     }
                     break;
                 case "Substring":
-                    var startIndex = Int32.Parse(args[0].ToString()) + 1;
+                    var startIndex = int.Parse(args[0].ToString()) + 1;
                     if (args.Count == 2)
                     {
-                        var length = Int32.Parse(args[1].ToString());
-                        statement = string.Format("substring({0} from {1} for {2})",
-                                                  quotedColName,
-                                                  startIndex,
-                                                  length);
+                        var length = int.Parse(args[1].ToString());
+                        statement = GetSubstringSql(quotedColName, startIndex, length);
                     }
                     else
-                        statement = string.Format("substring({0} from {1})",
-                                         quotedColName,
-                                         startIndex);
+                    {
+                        statement = GetSubstringSql(quotedColName, startIndex);
+                    }
                     break;
                 default:
                     throw new NotSupportedException();
             }
             return new PartialSqlString(statement);
         }
 
+        public virtual string GetSubstringSql(object quotedColumn, int startIndex, int? length = null)
+        {
+            return length != null
+                ? string.Format("substring({0} from {1} for {2})", quotedColumn, startIndex, length.Value)
+                : string.Format("substring({0} from {1})", quotedColumn, startIndex);
+        }
+
         public IDbDataParameter CreateParam(string name,
             object value = null,
             ParameterDirection direction = ParameterDirection.Input,

tests/ServiceStack.OrmLite.Tests/Expression/SelectFieldExpressionTests.cs

@@ -0,0 +1,37 @@
+using System.Linq;
+using NUnit.Framework;
+using ServiceStack.OrmLite.Tests.Shared;
+using ServiceStack.Text;
+
+namespace ServiceStack.OrmLite.Tests.Expression
+{
+    public class SelectFieldExpressionTests
+         : OrmLiteTestBase
+    {
+        [Test]
+        public void Can_Select_Substring()
+        {
+            using (var db = OpenDbConnection())
+            {
+                db.DropAndCreateTable<Person>();
+                db.InsertAll(Person.Rockstars);
+
+                var results = db.Select<Person>(x => x.FirstName.Substring(1, 2) == "im");
+
+                results.PrintDump();
+
+                var expected = Person.Rockstars.Where(x => x.FirstName.Substring(1, 2) == "im").ToList();
+
+                Assert.That(results.Count, Is.EqualTo(expected.Count));
+                Assert.That(results, Is.EquivalentTo(expected));
+
+                results = db.Select<Person>(x => x.FirstName.Substring(1) == "im");
+                results.PrintDump();
+
+                expected = Person.Rockstars.Where(x => x.FirstName.Substring(1) == "im").ToList();
+                Assert.That(results.Count, Is.EqualTo(expected.Count));
+                Assert.That(results, Is.EquivalentTo(expected));
+            }
+        }
+    }
+}

tests/ServiceStack.OrmLite.Tests/ServiceStack.OrmLite.Tests.csproj

@@ -127,6 +127,7 @@
     <Compile Include="Expression\FromExpressionTests.cs" />
     <Compile Include="Expression\GenericTableExpressions.cs" />
     <Compile Include="Expression\MethodExpressionTests.cs" />
+    <Compile Include="Expression\SelectFieldExpressionTests.cs" />
     <Compile Include="Expression\SqlExpressionParamTests.cs" />
     <Compile Include="Expression\SqlExpressionTests.cs" />
     <Compile Include="Expression\SelectExpressionTests.cs" />

tests/ServiceStack.OrmLite.Tests/Shared/Person.cs

@@ -5,12 +5,12 @@ namespace ServiceStack.OrmLite.Tests.Shared
     public class Person
     {
         public static Person[] Rockstars = new[] {
-            new Person(1, "Jimi", "Hendrix", 27), 
-            new Person(2, "Janis", "Joplin", 27), 
-            new Person(3, "Jim", "Morrisson", 27), 
-            new Person(4, "Kurt", "Cobain", 27),              
-            new Person(5, "Elvis", "Presley", 42), 
-            new Person(6, "Michael", "Jackson", 50), 
+            new Person(1, "Jimi", "Hendrix", 27),
+            new Person(2, "Janis", "Joplin", 27),
+            new Person(3, "Jim", "Morrisson", 27),
+            new Person(4, "Kurt", "Cobain", 27),
+            new Person(5, "Elvis", "Presley", 42),
+            new Person(6, "Michael", "Jackson", 50),
         };
 
         public int Id { get; set; }
@@ -26,6 +26,34 @@ public Person(int id, string firstName, string lastName, int age)
             LastName = lastName;
             Age = age;
         }
+
+        protected bool Equals(Person other)
+        {
+            return Id == other.Id && 
+                string.Equals(FirstName, other.FirstName) && 
+                string.Equals(LastName, other.LastName) && 
+                Age == other.Age;
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (ReferenceEquals(null, obj)) return false;
+            if (ReferenceEquals(this, obj)) return true;
+            if (obj.GetType() != this.GetType()) return false;
+            return Equals((Person)obj);
+        }
+
+        public override int GetHashCode()
+        {
+            unchecked
+            {
+                var hashCode = Id;
+                hashCode = (hashCode * 397) ^ (FirstName != null ? FirstName.GetHashCode() : 0);
+                hashCode = (hashCode * 397) ^ (LastName != null ? LastName.GetHashCode() : 0);
+                hashCode = (hashCode * 397) ^ Age;
+                return hashCode;
+            }
+        }
     }
 
     public class PersonWithAutoId