Fix for Dapper decimal support (#452)

Author: DarkWanderer

ClickHouse.Client.Tests/ORM/DapperTests.cs

@@ -175,4 +175,20 @@ public async Task ShouldExecuteSelectReturningDecimal()
         Assert.IsInstanceOf<decimal>(result);
         Assert.AreEqual(0.0001m, result);
     }
+
+    [Test]
+    public async Task ShouldInsertParameterizedFloat64Array()
+    {
+        const decimal expected = 123.456m;
+
+        await connection.ExecuteStatementAsync("TRUNCATE TABLE IF EXISTS test.dapper_decimal");
+        await connection.ExecuteStatementAsync("CREATE TABLE IF NOT EXISTS test.dapper_decimal (balance Decimal128(4)) ENGINE Memory");
+
+
+        var sql = @"INSERT INTO test.dapper_decimal (balance) VALUES (@balance)";
+        await connection.ExecuteAsync(sql, new { balance = expected });
+
+        var actual = (ClickHouseDecimal) await connection.ExecuteScalarAsync("SELECT * FROM test.dapper_decimal");
+        Assert.AreEqual(expected, actual.ToDecimal(CultureInfo.InvariantCulture));
+    }
 }

ClickHouse.Client.Tests/Types/TypeMappingTests.cs

@@ -67,7 +67,6 @@ public class TypeMappingTests
 
     [TestCase(typeof(float), ExpectedResult = "Float32")]
     [TestCase(typeof(double), ExpectedResult = "Float64")]
-    [TestCase(typeof(decimal), ExpectedResult = "Decimal128(0)")]
 
     [TestCase(typeof(string), ExpectedResult = "String")]
 

ClickHouse.Client/ADO/Parameters/ClickHouseDbParameter.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Data;
 using System.Data.Common;
+using ClickHouse.Client.Numerics;
 using ClickHouse.Client.Types;
 
 namespace ClickHouse.Client.ADO.Parameters;
@@ -33,7 +34,17 @@ public string QueryForm
     {
         get
         {
-            var chType = ClickHouseType ?? TypeConverter.ToClickHouseType(Value?.GetType() ?? typeof(DBNull)).ToString();
+            if (ClickHouseType != null)
+                return $"{{{ParameterName}:{ClickHouseType}}}";
+
+            if (Value is decimal d)
+            {
+                var parts = decimal.GetBits(d);
+                int scale = (parts[3] >> 16) & 0x7F;
+                return $"{{{ParameterName}:Decimal(22,{scale})}}";
+            }
+
+            var chType = TypeConverter.ToClickHouseType(Value?.GetType() ?? typeof(DBNull)).ToString();
             return $"{{{ParameterName}:{chType}}}";
         }
     }