Better StartsWith translation.

Author: cincuranet

src/FirebirdSql.EntityFrameworkCore.Firebird.Tests/Query/ElementaryTests.cs

@@ -183,6 +183,19 @@ public async Task SelectableProcedureWithParam()
 			Assert.DoesNotThrowAsync(() => query.LoadAsync());
 		}
 	}
+
+	[Test]
+	public async Task SelectStartsWithConstant()
+	{
+		await using (var db = await GetDbContext<SelectContext>())
+		{
+			var query = db.Set<MonAttachment>()
+				.Where(x => x.AttachmentName.StartsWith("Jiri"));
+			Assert.DoesNotThrowAsync(() => query.LoadAsync());
+			var sql = db.LastCommandText;
+			StringAssert.Contains("'Jiri%'", sql);
+		}
+	}
 }
 
 class SelectContext : FbTestDbContext

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

@@ -42,10 +42,14 @@ public SqlExpression Translate(SqlExpression instance, MethodInfo method, IReadO
 			return null;
 
 		var patternExpression = _fbSqlExpressionFactory.ApplyDefaultTypeMapping(arguments[0]);
+		var patternConstantExpression = patternExpression as SqlConstantExpression;
+		var likePatternExpression = patternConstantExpression != null
+			? (SqlExpression)_fbSqlExpressionFactory.Constant(((string)patternConstantExpression.Value) + "%")
+			: (SqlExpression)_fbSqlExpressionFactory.Add(patternExpression, _fbSqlExpressionFactory.Constant("%"));
 		var startsWithExpression = _fbSqlExpressionFactory.AndAlso(
 			_fbSqlExpressionFactory.Like(
 				instance,
-				_fbSqlExpressionFactory.Add(patternExpression, _fbSqlExpressionFactory.Constant("%"))),
+				likePatternExpression),
 			_fbSqlExpressionFactory.Equal(
 				_fbSqlExpressionFactory.ApplyDefaultTypeMapping(_fbSqlExpressionFactory.Function(
 					"LEFT",
@@ -61,9 +65,9 @@ public SqlExpression Translate(SqlExpression instance, MethodInfo method, IReadO
 					new[] { true, true },
 					instance.Type)),
 				patternExpression));
-		return patternExpression is SqlConstantExpression sqlConstantExpression
-			? (string)sqlConstantExpression.Value == string.Empty
-				? (SqlExpression)_fbSqlExpressionFactory.Constant(true)
+		return patternConstantExpression != null
+			? (string)patternConstantExpression.Value == string.Empty
+				? _fbSqlExpressionFactory.Constant(true)
 				: startsWithExpression
 			: _fbSqlExpressionFactory.OrElse(
 				startsWithExpression,