Improve exception message in case of duplicated column

src/NHibernate.Test/NHSpecificTest/GH1875/Fixture.cs

@@ -0,0 +1,63 @@
+using System;
+using NHibernate.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH1875
+{
+	public class BadlyMappedEntity
+	{
+		public virtual Guid Id { get; set; }
+		public virtual long FirstValue { get; set; }
+		public virtual long SecondValue { get; set; }
+	}
+
+	[TestFixture]
+	public class Fixture
+	{
+		protected HbmMapping GetMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<BadlyMappedEntity>(
+				ca =>
+				{
+					ca.Abstract(true);
+					ca.Id(
+						x => x.Id,
+						map =>
+						{
+							map.Column("BadlyMappedEntityId");
+							map.Generator(Generators.GuidComb);
+						});
+					ca.Property(x => x.FirstValue, map => map.Column("SameColumn"));
+					// SecondValue is mapped with same name as another column, this gives the AbstractEntityMapper
+					// more entries in the fields array than there are in the includeColumns array; this causes the
+					// index to fall out of bounds.
+					ca.Property(x => x.SecondValue, map => map.Column("SameColumn"));
+				});
+
+			return mapper.CompileMappingFor(new[] { typeof(BadlyMappedEntity) });
+		}
+
+		[Test]
+		public void ShouldThrowSoundErrorForBadlyMappedEntity()
+		{
+			var mappings = GetMappings();
+			var cfg = TestConfigurationHelper.GetDefaultConfiguration();
+			cfg.AddMapping(mappings);
+
+			ISessionFactory factory = null;
+			try
+			{
+				Assert.That(
+					() => factory = cfg.BuildSessionFactory(),
+					Throws.TypeOf<MappingException>().And.Message.Contains("BadlyMappedEntity").And.InnerException
+					      .Message.Contains("SameColumn"));
+			}
+			finally
+			{
+				factory?.Dispose();
+			}
+		}
+	}
+}

src/NHibernate/Async/Persister/Entity/AbstractEntityPersister.cs

@@ -14,7 +14,6 @@
 using System.Data;
 using System.Data.Common;
 using System.Text;
-
 using NHibernate.AdoNet;
 using NHibernate.Cache;
 using NHibernate.Cache.Entry;
@@ -30,7 +29,6 @@
 using NHibernate.Metadata;
 using NHibernate.Properties;
 using NHibernate.SqlCommand;
-using NHibernate.Tuple;
 using NHibernate.Tuple.Entity;
 using NHibernate.Type;
 using NHibernate.Util;

src/NHibernate/Persister/Entity/AbstractEntityPersister.cs

@@ -4,7 +4,6 @@
 using System.Data;
 using System.Data.Common;
 using System.Text;
-
 using NHibernate.AdoNet;
 using NHibernate.Cache;
 using NHibernate.Cache.Entry;
@@ -20,7 +19,6 @@
 using NHibernate.Metadata;
 using NHibernate.Properties;
 using NHibernate.SqlCommand;
-using NHibernate.Tuple;
 using NHibernate.Tuple.Entity;
 using NHibernate.Type;
 using NHibernate.Util;
@@ -2279,7 +2277,17 @@ protected internal SqlCommandInfo GenerateUpdateString(bool[] includeProperty, i
 				if (includeProperty[i] && IsPropertyOfTable(i, j))
 				{
 					// this is a property of the table, which we are updating
-					updateBuilder.AddColumns(GetPropertyColumnNames(i), propertyColumnUpdateable[i], PropertyTypes[i]);
+					try
+					{
+						updateBuilder.AddColumns(GetPropertyColumnNames(i), propertyColumnUpdateable[i], PropertyTypes[i]);
+					}
+					catch (ArgumentException arex)
+					{
+						throw new MappingException(
+							$"Unable to build the update statement for class {entityMetamodel.Name}: " +
+							$"a failure occured when adding the property {PropertyNames[i]}",
+							arex);
+					}
 					hasColumns = hasColumns || GetPropertyColumnSpan(i) > 0;
 				}
 			}
@@ -2368,24 +2376,54 @@ protected virtual SqlCommandInfo GenerateInsertString(bool identityInsert, bool[
 				if (includeProperty[i] && IsPropertyOfTable(i, j))
 				{
 					// this property belongs on the table and is to be inserted
-					builder.AddColumns(GetPropertyColumnNames(i), propertyColumnInsertable[i], PropertyTypes[i]);
+					try
+					{
+						builder.AddColumns(GetPropertyColumnNames(i), propertyColumnInsertable[i], PropertyTypes[i]);
+					}
+					catch (ArgumentException arex)
+					{
+						throw new MappingException(
+							$"Unable to build the insert statement for class {entityMetamodel.Name}: " +
+							$"a failure occured when adding the property {PropertyNames[i]}",
+							arex);
+					}
 				}
 			}
 
 			// add the discriminator
 			if (j == 0)
 			{
-				AddDiscriminatorToInsert(builder);
+				try
+				{
+					AddDiscriminatorToInsert(builder);
+				}
+				catch (ArgumentException arex)
+				{
+					throw new MappingException(
+						$"Unable to build the insert statement for class {entityMetamodel.Name}: " +
+						"a failure occured when adding the discriminator",
+						arex);
+				}
 			}
 
 			// add the primary key
-			if (j == 0 && identityInsert)
+			try
 			{
-				builder.AddIdentityColumn(GetKeyColumns(0)[0]);
+				if (j == 0 && identityInsert)
+				{
+					builder.AddIdentityColumn(GetKeyColumns(0)[0]);
+				}
+				else
+				{
+					builder.AddColumns(GetKeyColumns(j), null, GetIdentifierType(j));
+				}
 			}
-			else
+			catch (ArgumentException arex)
 			{
-				builder.AddColumns(GetKeyColumns(j), null, GetIdentifierType(j));
+				throw new MappingException(
+					$"Unable to build the insert statement for class {entityMetamodel.Name}: " +
+					"a failure occured when adding the Id of the class",
+					arex);
 			}
 
 			if (Factory.Settings.IsCommentsEnabled)

src/NHibernate/SqlCommand/SqlInsertBuilder.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 
 using NHibernate.Engine;
@@ -55,7 +56,7 @@ public virtual SqlInsertBuilder AddColumn(string columnName, IType propertyType)
 			SqlType[] sqlTypes = propertyType.SqlTypes(factory);
 			if (sqlTypes.Length > 1)
 				throw new AssertionFailure("Adding one column for a composed IType.");
-			columns[columnName] = sqlTypes[0];
+			AddColumnWithValueOrType(columnName, sqlTypes[0]);
 			return this;
 		}
 
@@ -80,7 +81,7 @@ public SqlInsertBuilder AddColumn(string columnName, object val, ILiteralType li
 		/// <returns>The SqlInsertBuilder.</returns>
 		public SqlInsertBuilder AddColumn(string columnName, string val)
 		{
-			columns[columnName] = val;
+			AddColumnWithValueOrType(columnName, val);
 			return this;
 		}
 
@@ -94,13 +95,22 @@ public SqlInsertBuilder AddColumns(string[] columnNames, bool[] insertable, ITyp
 				{
 					if (i >= sqlTypes.Length)
 						throw new AssertionFailure("Different columns and it's IType.");
-					columns[columnNames[i]] = sqlTypes[i];
+					AddColumnWithValueOrType(columnNames[i], sqlTypes[i]);
 				}
 			}
 
 			return this;
 		}
 
+		private void AddColumnWithValueOrType(string columnName, object valueOrType)
+		{
+			if (columns.ContainsKey(columnName))
+				throw new ArgumentException(
+					$"The column '{columnName}' has already been added in this SQL builder",
+					nameof(columnName));
+			columns.Add(columnName, valueOrType);
+		}
+
 		public virtual SqlInsertBuilder AddIdentityColumn(string columnName)
 		{
 			string value = Dialect.IdentityInsertString;

src/NHibernate/SqlCommand/SqlUpdateBuilder.cs

@@ -61,7 +61,7 @@ public SqlUpdateBuilder AddColumn(string columnName, object val, ILiteralType li
 		/// <returns>The SqlUpdateBuilder.</returns>
 		public SqlUpdateBuilder AddColumn(string columnName, string val)
 		{
-			columns[columnName] = val;
+			AddColumnWithValueOrType(columnName, val);
 			return this;
 		}
 
@@ -74,7 +74,7 @@ public SqlUpdateBuilder AddColumn(string columnName, string val)
 		public SqlUpdateBuilder AddColumns(string[] columnsName, string val)
 		{
 			foreach (string columnName in columnsName)
-				columns[columnName] = val;
+				AddColumnWithValueOrType(columnName, val);
 
 			return this;
 		}
@@ -84,7 +84,7 @@ public virtual SqlUpdateBuilder AddColumn(string columnName, IType propertyType)
 			SqlType[] sqlTypes = propertyType.SqlTypes(Mapping);
 			if (sqlTypes.Length > 1)
 				throw new AssertionFailure("Adding one column for a composed IType.");
-			columns[columnName] = sqlTypes[0];
+			AddColumnWithValueOrType(columnName, sqlTypes[0]);
 			return this;
 		}
 
@@ -115,13 +115,22 @@ public SqlUpdateBuilder AddColumns(string[] columnNames, bool[] updateable, ITyp
 				{
 					if (i >= sqlTypes.Length)
 						throw new AssertionFailure("Different columns and it's IType.");
-					columns[columnNames[i]] = sqlTypes[i];
+					AddColumnWithValueOrType(columnNames[i], sqlTypes[i]);
 				}
 			}
 
 			return this;
 		}
 
+		private void AddColumnWithValueOrType(string columnName, object valueOrType)
+		{
+			if (columns.ContainsKey(columnName))
+				throw new ArgumentException(
+					$"The column '{columnName}' has already been added in this SQL builder",
+					nameof(columnName));
+			columns.Add(columnName, valueOrType);
+		}
+
 		public SqlUpdateBuilder AppendAssignmentFragment(SqlString fragment)
 		{
 			// SqlString is immutable