More tests.

src/FirebirdSql.EntityFrameworkCore.Firebird.FunctionalTests/Query/GearsOfWarQueryFbTest.cs

@@ -411,6 +411,13 @@ public override Task DateTimeOffset_to_unix_time_seconds(bool async)
 		return base.DateTimeOffset_to_unix_time_seconds(async);
 	}
 
+	[NotSupportedByProviderTheory]
+	[MemberData(nameof(IsAsyncData))]
+	public override Task Non_string_concat_uses_appropriate_type_mapping(bool async)
+	{
+		return base.Non_string_concat_uses_appropriate_type_mapping(async);
+	}
+
 	[Theory(Skip = "NETProvider#1008")]
 	[MemberData(nameof(IsAsyncData))]
 	public override Task Where_TimeOnly_IsBetween(bool async)

src/FirebirdSql.EntityFrameworkCore.Firebird/Query/ExpressionTranslators/Internal/FbDateOnlyMethodTranslator.cs

@@ -25,7 +25,7 @@
 
 namespace FirebirdSql.EntityFrameworkCore.Firebird.Query.ExpressionTranslators.Internal;
 
-public class SqlServerDateOnlyMethodTranslator : IMethodCallTranslator
+public class FbDateOnlyMethodTranslator : IMethodCallTranslator
 {
 	readonly Dictionary<MethodInfo, string> _methodInfoDatePartMapping = new()
 	{
@@ -36,7 +36,7 @@ public class SqlServerDateOnlyMethodTranslator : IMethodCallTranslator
 
 	readonly ISqlExpressionFactory _sqlExpressionFactory;
 
-	public SqlServerDateOnlyMethodTranslator(ISqlExpressionFactory sqlExpressionFactory)
+	public FbDateOnlyMethodTranslator(ISqlExpressionFactory sqlExpressionFactory)
 	{
 		_sqlExpressionFactory = sqlExpressionFactory;
 	}

src/FirebirdSql.EntityFrameworkCore.Firebird/Query/ExpressionTranslators/Internal/FbObjectToStringTranslator.cs

@@ -33,7 +33,6 @@ public class FbObjectToStringTranslator : IMethodCallTranslator
 			typeof(int),
 			typeof(long),
 			typeof(DateTime),
-			typeof(bool),
 			typeof(byte),
 			typeof(byte[]),
 			typeof(double),
@@ -59,18 +58,54 @@ public FbObjectToStringTranslator(FbSqlExpressionFactory fbSqlExpressionFactory)
 
 	public SqlExpression Translate(SqlExpression instance, MethodInfo method, IReadOnlyList<SqlExpression> arguments, IDiagnosticsLogger<DbLoggerCategory.Query> logger)
 	{
-		if (method.Name == nameof(ToString) && method.GetParameters().Length == 0)
+		if (instance == null || method.Name != nameof(ToString) || arguments.Count != 0)
 		{
-			var type = instance.Type.UnwrapNullableType();
-			if (SupportedTypes.Contains(type))
+			return null;
+		}
+
+		if (instance.TypeMapping?.ClrType == typeof(string))
+		{
+			return instance;
+		}
+
+		if (SupportedTypes.Contains(instance.Type))
+		{
+			return _fbSqlExpressionFactory.Convert(instance, typeof(string));
+		}
+		else if (instance.Type == typeof(Guid))
+		{
+			return _fbSqlExpressionFactory.Function("UUID_TO_CHAR", new[] { instance }, true, new[] { true }, typeof(string));
+		}
+		else if (instance.Type == typeof(bool))
+		{
+			if (instance is not ColumnExpression { IsNullable: false })
 			{
-				return _fbSqlExpressionFactory.Convert(instance, typeof(string));
+				return _fbSqlExpressionFactory.Case(
+					instance,
+					new[]
+					{
+						new CaseWhenClause(
+							_fbSqlExpressionFactory.Constant(false),
+							_fbSqlExpressionFactory.Constant(false.ToString())),
+						new CaseWhenClause(
+							_fbSqlExpressionFactory.Constant(true),
+							_fbSqlExpressionFactory.Constant(true.ToString()))
+					},
+					_fbSqlExpressionFactory.Constant(string.Empty));
 			}
-			else if (type == typeof(Guid))
+			else
 			{
-				return _fbSqlExpressionFactory.Function("UUID_TO_CHAR", new[] { instance }, true, new[] { true }, typeof(string));
+				return _fbSqlExpressionFactory.Case(
+					new[]
+					{
+						new CaseWhenClause(
+							instance,
+							_fbSqlExpressionFactory.Constant(true.ToString()))
+					},
+					_fbSqlExpressionFactory.Constant(false.ToString()));
 			}
 		}
+
 		return null;
 	}
 }

src/FirebirdSql.EntityFrameworkCore.Firebird/Query/ExpressionTranslators/Internal/FbTimeOnlyMethodTranslator.cs

@@ -0,0 +1,60 @@
+/*
+ *    The contents of this file are subject to the Initial
+ *    Developer's Public License Version 1.0 (the "License");
+ *    you may not use this file except in compliance with the
+ *    License. You may obtain a copy of the License at
+ *    https://github.com/FirebirdSQL/NETProvider/raw/master/license.txt.
+ *
+ *    Software distributed under the License is distributed on
+ *    an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either
+ *    express or implied. See the License for the specific
+ *    language governing rights and limitations under the License.
+ *
+ *    All Rights Reserved.
+ */
+
+//$Authors = Jiri Cincura ([email protected])
+
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Diagnostics;
+using Microsoft.EntityFrameworkCore.Query;
+using Microsoft.EntityFrameworkCore.Query.SqlExpressions;
+
+namespace FirebirdSql.EntityFrameworkCore.Firebird.Query.ExpressionTranslators.Internal;
+
+public class FbTimeOnlyMethodTranslator : IMethodCallTranslator
+{
+	static readonly MethodInfo FromDateTime = typeof(TimeOnly).GetRuntimeMethod(nameof(TimeOnly.FromDateTime), [typeof(DateTime)]);
+	static readonly MethodInfo FromTimeSpan = typeof(TimeOnly).GetRuntimeMethod(nameof(TimeOnly.FromTimeSpan), [typeof(TimeSpan)]);
+
+	readonly ISqlExpressionFactory _sqlExpressionFactory;
+
+	public FbTimeOnlyMethodTranslator(ISqlExpressionFactory sqlExpressionFactory)
+	{
+		_sqlExpressionFactory = sqlExpressionFactory;
+	}
+
+	public virtual SqlExpression Translate(
+		SqlExpression instance,
+		MethodInfo method,
+		IReadOnlyList<SqlExpression> arguments,
+		IDiagnosticsLogger<DbLoggerCategory.Query> logger)
+	{
+		if (method.DeclaringType != typeof(TimeOnly))
+		{
+			return null;
+		}
+
+		if ((method == FromDateTime || method == FromTimeSpan)
+			&& instance is null
+			&& arguments.Count == 1)
+		{
+			return _sqlExpressionFactory.Convert(arguments[0], typeof(TimeOnly));
+		}
+
+		return null;
+	}
+}

src/FirebirdSql.EntityFrameworkCore.Firebird/Query/Internal/FbQuerySqlGenerator.cs

@@ -201,7 +201,7 @@ protected override Expression VisitSqlConstant(SqlConstantExpression sqlConstant
 
 	protected override void GenerateEmptyProjection(SelectExpression selectExpression)
 	{
-		base.GenerateEmptyProjection(selectExpression);
+		Sql.Append("1 AS dummy");
 		if (selectExpression.Alias != null)
 		{
 			Sql.Append(" AS empty");