Support for value converter attribute (#408)

* Column value converter attribute support

* Revert "Column value converter attribute support"

This reverts commit 7a5b050.

* Column value converter attribute support

PetaPoco.Tests.Unit/Core/ConventionMapperTests.cs

@@ -33,6 +33,20 @@ public void GetToDbConverter_GivenProperty_ShouldBeNull()
             func.ShouldBeNull();
         }
 
+        [Fact]
+        public void GetFromDbConverter_GivenPropertyWithValueConverterAttribute_ShouldNotBeNull()
+        {
+            var func = _mapper.GetFromDbConverter(typeof(Order).GetProperty(nameof(Order.PO)), typeof(string));
+            func.ShouldNotBeNull();
+        }
+
+        [Fact]
+        public void GetToDbConverter_GivenPropertyWithValueConverterAttribute_ShouldNotBeNull()
+        {
+            var func = _mapper.GetToDbConverter(typeof(Order).GetProperty(nameof(Order.PO)));
+            func.ShouldNotBeNull();
+        }
+
         [Fact]
         public void GetFromDbConverter_GivenPropertyTypeAndInterceptSet_ShouldCallback()
         {
@@ -209,12 +223,27 @@ public class EntityWithAttributes
             public string ColumnTwo { get; set; }
         }
 
+        public class EmptyValueConverterAttribute : ValueConverterAttribute
+        {
+            public override object ConvertFromDb(object value)
+            {
+                return value;
+            }
+
+            public override object ConvertToDb(object value)
+            {
+                return value;
+            }
+        }
+
+
         public class Order
         {
             public long OrderId { get; set; }
 
             public DateTime CreatedOn { get; set; }
 
+            [EmptyValueConverter]
             public string PO { get; set; }
 
             public decimal? Discount { get; set; }

PetaPoco/Attributes/ValueConverterAttribute.cs

@@ -0,0 +1,30 @@
+// <copyright company="PetaPoco - CollaboratingPlatypus">
+//      Apache License, Version 2.0 https://github.com/CollaboratingPlatypus/PetaPoco/blob/master/LICENSE.txt
+// </copyright>
+// <author>PetaPoco - CollaboratingPlatypus</author>
+// <date>2017/07/20</date>
+
+using System;
+
+namespace PetaPoco
+{
+    /// <summary>
+    /// Represents an attribute which can decorate a Poco property conver value from database type to property type and conversely.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Property)]
+    public abstract class ValueConverterAttribute : Attribute
+    {
+        /// <summary>
+        /// Function to convert property value to database type value.
+        /// </summary>
+        /// <param name="value">Property value</param>
+        /// <returns>Converted database value</returns>
+        public abstract object ConvertToDb(object value);
+        /// <summary>
+        /// Function to convert database value to property type value.
+        /// </summary>
+        /// <param name="value">Database value</param>
+        /// <returns>Converted property type value</returns>
+        public abstract object ConvertFromDb(object value);
+    }
+}

PetaPoco/Core/ConventionMapper.cs

@@ -155,6 +155,20 @@ public ConventionMapper()
 
                 return true;
             };
+            FromDbConverter = (pi, t) =>
+            {
+                var valueConverter = pi.GetCustomAttributes(typeof(ValueConverterAttribute), true).FirstOrDefault() as ValueConverterAttribute;
+                if (valueConverter != null)
+                    return valueConverter.ConvertFromDb;
+                return null;
+            };
+            ToDbConverter = (pi) =>
+            {
+                var valueConverter = pi.GetCustomAttributes(typeof(ValueConverterAttribute), true).FirstOrDefault() as ValueConverterAttribute;
+                if (valueConverter != null)
+                    return valueConverter.ConvertToDb;
+                return null;
+            };
         }
 
         /// <summary>

PetaPoco/PetaPoco.csproj

@@ -50,6 +50,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Attributes\ColumnAttribute.cs" />
+    <Compile Include="Attributes\ValueConverterAttribute.cs" />
     <Compile Include="Core\AnsiString.cs" />
     <Compile Include="Core\ColumnInfo.cs" />
     <Compile Include="Core\ConventionMapper.cs" />