fix comments

Author: nikitam

src/EFCore.Ydb/src/Query/Internal/YdbSqlExpressionFactory.cs

@@ -17,22 +17,25 @@ public override SqlExpression Coalesce(SqlExpression left, SqlExpression right,
         RelationalTypeMapping? typeMapping = null)
     {
         // For .Sum(x => x.Decimal) EF generates coalesce(sum(x.Decimal), 0.0)) because SUM must have value
-        var funcExpression = left as SqlFunctionExpression;
-        var constExpression = right as SqlConstantExpression;
-        
-        if (funcExpression != null && constExpression != null && constExpression.TypeMapping != null
+
+        if (left is SqlFunctionExpression funcExpression 
+            && 
+            right is SqlConstantExpression constExpression && constExpression.TypeMapping != null
             &&
             funcExpression.Name.Equals("SUM", StringComparison.OrdinalIgnoreCase)
             &&
+            funcExpression.Arguments != null
+            &&
             constExpression.TypeMapping.DbType == DbType.Decimal
             &&
             constExpression.Value != null)
         {
+            // get column expression for SUM function expression
+            var columnExpression = funcExpression.Arguments[0] as ColumnExpression;
+
             var correctRight = new SqlConstantExpression(constExpression.Value,
-                YdbDecimalTypeMapping.WithMaxPrecision); // in the feature change static max precision/scale to
-                                                         // to dynamically created correct precision/scale
-                                                         // it depends on db scheme and can not correctly define only in code
-            
+                YdbDecimalTypeMapping.GetWithMaxPrecision(columnExpression?.TypeMapping?.Scale)); 
+
             return base.Coalesce(left, correctRight, typeMapping);
         }
 

src/EFCore.Ydb/src/Storage/Internal/Mapping/YdbDecimalTypeMapping.cs

@@ -12,26 +12,15 @@ public class YdbDecimalTypeMapping : DecimalTypeMapping
 
     public new static YdbDecimalTypeMapping Default => new();
 
-    static YdbDecimalTypeMapping()
-    {
-        WithMaxPrecision = GetWithMaxPrecision();
-    }
-    
-    public static YdbDecimalTypeMapping WithMaxPrecision { get; }
-
-    private static YdbDecimalTypeMapping GetWithMaxPrecision()
-    {
-        var result = new YdbDecimalTypeMapping(new RelationalTypeMappingParameters(
-                new CoreTypeMappingParameters(
-                    typeof(decimal)),
-                    storeType: "Decimal",
-                    dbType: System.Data.DbType.Decimal,
-                    precision: MaxPrecision,
-                    scale: DefaultScale)
-            );
-        
-        return result;
-    }
+    public static YdbDecimalTypeMapping GetWithMaxPrecision(int? scale) =>
+        new(new RelationalTypeMappingParameters(
+            new CoreTypeMappingParameters(
+                typeof(decimal)),
+            storeType: "Decimal",
+            dbType: System.Data.DbType.Decimal,
+            precision: MaxPrecision,
+            scale: scale ?? DefaultScale)
+        );
 
     public YdbDecimalTypeMapping() : this(
         new RelationalTypeMappingParameters(
@@ -65,8 +54,5 @@ protected override void ConfigureParameter(DbParameter parameter)
             parameter.Scale = (byte)s;
     }
 
-    protected override string GenerateNonNullSqlLiteral(object value)
-    {
-        return $"Decimal('{base.GenerateNonNullSqlLiteral(value)}', {this.Precision ?? MaxPrecision}, {this.Scale ?? DefaultScale})";
-    }
+    protected override string GenerateNonNullSqlLiteral(object value) => $"Decimal('{base.GenerateNonNullSqlLiteral(value)}', {this.Precision ?? MaxPrecision}, {this.Scale ?? DefaultScale})";
 }