Improve some sparse arrays

Author: Alexander Kot

src/NHibernate/Loader/Loader.cs

@@ -82,7 +82,7 @@ public sealed class QueryCacheInfo
 		/// <summary>
 		/// Caches subclass entity aliases for given persister index in <see cref="EntityPersisters"/>  and subclass entity name
 		/// </summary>
-		private readonly ConcurrentDictionary<Tuple<int, string>, string[][]> _subclassEntityAliasesMap = new ConcurrentDictionary<Tuple<int, string>, string[][]>();
+		private readonly Lazy<ConcurrentDictionary<Tuple<int, string>, string[][]>> _subclassEntityAliasesMap = new(()=>new ConcurrentDictionary<Tuple<int, string>, string[][]>());
 
 		protected Loader(ISessionFactoryImplementor factory)
 		{
@@ -1322,7 +1322,7 @@ private void LoadFromResultSet(DbDataReader rs, int i, object obj, ILoadable per
 		private string[][] GetSubclassEntityAliases(int i, ILoadable persister)
 		{
 			var cacheKey = System.Tuple.Create(i, persister.EntityName);
-			return _subclassEntityAliasesMap.GetOrAdd(
+			return _subclassEntityAliasesMap.Value.GetOrAdd(
 				cacheKey,
 				k => EntityAliases[i].GetSuffixedPropertyAliases(persister));
 		}

src/NHibernate/Mapping/Constraint.cs

@@ -15,7 +15,7 @@ namespace NHibernate.Mapping
 	public abstract class Constraint : IRelationalModel
 	{
 		private string name;
-		private readonly List<Column> columns = new List<Column>();
+		private readonly List<Column> columns = new List<Column>(1);
 		private Table table;
 
 		/// <summary>

src/NHibernate/Mapping/ForeignKey.cs

@@ -2,6 +2,7 @@
 using System.Text;
 using NHibernate.Util;
 using System;
+using System.Linq;
 
 namespace NHibernate.Mapping
 {
@@ -14,7 +15,7 @@ public class ForeignKey : Constraint
 		private Table referencedTable;
 		private string referencedEntityName;
 		private bool cascadeDeleteEnabled;
-		private readonly List<Column> referencedColumns = new List<Column>();
+		private List<Column> referencedColumns;
 
 		/// <summary>
 		/// Generates the SQL string to create the named Foreign Key Constraint in the database.
@@ -35,7 +36,7 @@ public override string SqlConstraintString(Dialect.Dialect d, string constraintN
 			if (IsReferenceToPrimaryKey)
 				refiter = referencedTable.PrimaryKey.ColumnIterator;
 			else
-				refiter = referencedColumns;
+				refiter = referencedColumns ?? Enumerable.Empty<Column>();
 			foreach (Column column in ColumnIterator)
 			{
 				cols[i] = column.GetQuotedName(d);
@@ -172,13 +173,14 @@ public virtual void AddReferencedColumns(IEnumerable<Column> referencedColumnsIt
 
 		private void AddReferencedColumn(Column column)
 		{
+			referencedColumns ??= new List<Column>(1);
 			if (!referencedColumns.Contains(column))
 				referencedColumns.Add(column);
 		}
 
 		internal void AddReferencedTable(PersistentClass referencedClass)
 		{
-			if (referencedColumns.Count > 0)
+			if (referencedColumns != null && referencedColumns.Count > 0)
 			{
 				referencedTable = referencedColumns[0].Value.Table;
 			}
@@ -199,7 +201,7 @@ public override string ToString()
 					.Append(string.Join(", ", Columns))
 					.Append(" ref-columns:")
 					.Append('(')
-					.Append(string.Join(", ", ReferencedColumns))
+					.Append(string.Join(", ", ReferencedColumnsReadOnly))
 					.Append(") as ")
 					.Append(Name);
 				return result.ToString();
@@ -218,7 +220,16 @@ public bool HasPhysicalConstraint
 
 		public IList<Column> ReferencedColumns
 		{
-			get { return referencedColumns; }
+			get
+			{	
+				referencedColumns ??= new List<Column>(1);
+				return referencedColumns;
+			}
+		}
+
+		private IEnumerable<Column> ReferencedColumnsReadOnly
+		{
+			get { return referencedColumns ?? Enumerable.Empty<Column>(); }
 		}
 
 		public string ReferencedEntityName
@@ -230,7 +241,7 @@ public string ReferencedEntityName
 		/// <summary>Does this foreignkey reference the primary key of the reference table </summary>
 		public bool IsReferenceToPrimaryKey
 		{
-			get { return referencedColumns.Count == 0; }
+			get { return referencedColumns == null || referencedColumns.Count == 0; }
 		}
 
 		public string GeneratedConstraintNamePrefix => "FK_";
@@ -242,7 +253,7 @@ public override bool IsGenerated(Dialect.Dialect dialect)
 			if (dialect.SupportsNullInUnique || IsReferenceToPrimaryKey)
 				return true;
 
-			foreach (var column in ReferencedColumns)
+			foreach (var column in ReferencedColumnsReadOnly)
 			{
 				if (column.IsNullable)
 					return false;

src/NHibernate/Mapping/Index.cs

@@ -14,7 +14,7 @@ namespace NHibernate.Mapping
 	public class Index : IRelationalModel
 	{
 		private Table table;
-		private readonly List<Column> columns = new List<Column>();
+		private readonly List<Column> columns = new List<Column>(1);
 		private string name;
 
 		public static string BuildSqlCreateIndexString(Dialect.Dialect dialect, string name, Table table,

src/NHibernate/Mapping/SimpleValue.cs

@@ -15,7 +15,7 @@ namespace NHibernate.Mapping
 	[Serializable]
 	public class SimpleValue : IKeyValue
 	{
-		private readonly List<ISelectable> columns = new List<ISelectable>();
+		private readonly List<ISelectable> columns = new List<ISelectable>(1);
 		private IType type;
 		private IDictionary<string, string> typeParameters;
 

src/NHibernate/Mapping/Table.cs

@@ -1064,9 +1064,12 @@ internal ForeignKeyKey(IEnumerable<Column> columns, string referencedClassName,
 			{
 				this.referencedClassName = referencedClassName;
 				this.columns = new List<Column>(columns);
+				this.columns.TrimExcess();
+
 				if (referencedColumns != null)
 				{
 					this.referencedColumns = new List<Column>(referencedColumns);
+					this.referencedColumns.TrimExcess();
 				}
 				else
 				{

src/NHibernate/SqlCommand/SqlString.cs

@@ -215,6 +215,9 @@ internal SqlString(IEnumerable<object> parts)
 			_firstPartIndex = _parts.Count > 0 ? 0 : -1;
 			_lastPartIndex = _parts.Count - 1;
 			_length = sqlIndex;
+
+			_parts.TrimExcess();
+			_parameters.TrimExcess();
 		}
 
 		#endregion