Update README.md

README.md

@@ -30,6 +30,27 @@ Finally, call the SeedFromResource extension method:
 
 You also have the option to seed from a csv file on disk using SeedFromFile, or from any stream using SeedFromStream.
 
+##Connecting Related Entities
+Loading data from a CSV file can be a little more complicated when there are relationships between the entities were are loading. Take Countries and Provinces/States as an example. A Province/State always belongs to a single Country. In this case, create a CSV file that includes the Country Code of the Country that the Province State belongs to:
+
+    CountryCode,Code,Name
+    CA,SK,Saskatchewan
+    CA,AB,Alberta
+    US,AZ,Arizona
+    US,AR,Arkansas
+    US,CA,California
+
+Now, specify a custom mapping action when seeding from the provinces csv:
+
+    context.Countries.SeedFromResource("MyProject.SeedData.countries.csv", c => c.Code);
+    context.SaveChanges();
+    context.ProvinceStates.SeedFromResource("MyProject.SeedData.provincestates.csv", p => p.Code,
+            new CsvColumnMapping<ProvinceState>("CountryCode", (state, countryCode) =>
+                {
+                    state.Country = context.Countries.Single(c => c.Code == countryCode);
+                })
+             );       
+
 ##Available on Nuget
 PM> Install-Package EntityFramework.Seeder.EF6