fix: 历史汇率处理bug + Transaction表增加汇率字段

关键修复：
1. BackfillNavHistoryInternalAsync 汇率处理bug
   - holdings 存储目标币种成本，避免卖出时用当前汇率重转历史成本
   - 优先使用交易时保存的汇率

2. Transaction 表新增字段
   - exchange_rate: 交易时汇率
   - total_amount_base: 本位币金额
   - 创建交易时自动保存汇率

3. CalculateAndSaveDailyNavAsync
   - 优先使用 TotalAmountBase 字段计算成本
   - 回退到当前汇率（兼容历史数据）

4. 新增迁移脚本 sql/migrate_financial_fields.sql

AssetManager.Data/Transaction.cs

@@ -57,7 +57,7 @@ public class Transaction
     public decimal Price { get; set; }
     
     /// <summary>
-    /// 交易总金额
+    /// 交易总金额（原始币种）
     /// </summary>
     [SugarColumn(ColumnName = "total_amount", ColumnDataType = "decimal(18,4)")]
     public decimal TotalAmount { get; set; }
@@ -68,6 +68,20 @@ public class Transaction
     [SugarColumn(ColumnName = "currency", Length = 10)]
     public string? Currency { get; set; }
     
+    /// <summary>
+    /// 交易时汇率（原始币种 -> 组合本位币）
+    /// 用于精确计算历史净值，避免汇率变化影响
+    /// </summary>
+    [SugarColumn(ColumnName = "exchange_rate", ColumnDataType = "decimal(18,6)", IsNullable = true)]
+    public decimal? ExchangeRate { get; set; }
+    
+    /// <summary>
+    /// 交易总金额（组合本位币）
+    /// = TotalAmount * ExchangeRate，用于精确计算
+    /// </summary>
+    [SugarColumn(ColumnName = "total_amount_base", ColumnDataType = "decimal(18,4)", IsNullable = true)]
+    public decimal? TotalAmountBase { get; set; }
+    
     /// <summary>
     /// 交易状态 (processing/completed)
     /// </summary>

AssetManager.Services/PortfolioNavService.cs

@@ -199,9 +199,23 @@ public class PortfolioNavService : IPortfolioNavService
             
             if (tx.Type == "buy")
             {
-                decimal txAmount = tx.TotalAmount;
-                decimal txAmountInTarget = await _exchangeRateService.ConvertAmountAsync(
-                    txAmount, tx.Currency, targetCurrency);
+                // 优先使用交易时保存的本位币金额，确保历史净值计算一致
+                decimal txAmountInTarget;
+                if (tx.TotalAmountBase.HasValue && tx.TotalAmountBase > 0)
+                {
+                    txAmountInTarget = tx.TotalAmountBase.Value;
+                    _logger.LogDebug("使用交易时汇率: {StockCode}, 金额={Amount}, 本位币金额={BaseAmount}", 
+                        tx.StockCode, tx.TotalAmount, txAmountInTarget);
+                }
+                else
+                {
+                    // 回退到当前汇率（历史数据可能不准确）
+                    txAmountInTarget = await _exchangeRateService.ConvertAmountAsync(
+                        tx.TotalAmount, tx.Currency, targetCurrency);
+                    _logger.LogDebug("使用当前汇率: {StockCode}, 金额={Amount}, 本位币金额={BaseAmount}", 
+                        tx.StockCode, tx.TotalAmount, txAmountInTarget);
+                }
+                
                 totalCost += txAmountInTarget;
                 
                 // 更新该标的的累计成本和数量
@@ -342,10 +356,11 @@ public class PortfolioNavService : IPortfolioNavService
                 .ExecuteCommandAsync();
         }
 
-        // 持仓快照：股票代码 -> (数量, 成本)
-        var holdings = new Dictionary<string, (decimal shares, decimal cost, string? currency, string? assetType)>();
+        // 持仓快照：股票代码 -> (数量, 成本[目标币种], 原始币种, 资产类型)
+        // 关键修复：成本存储为目标币种，避免卖出时用当前汇率重新转换历史成本
+        var holdings = new Dictionary<string, (decimal shares, decimal costInTargetCurrency, string? currency, string? assetType)>();
 
-        // 累计投入成本
+        // 累计投入成本（目标币种）
         decimal cumulativeCost = 0;
 
         // 记录创建数量
@@ -372,21 +387,31 @@ public class PortfolioNavService : IPortfolioNavService
 
                 if (tx.Type == "buy")
                 {
+                    // 优先使用交易时保存的本位币金额，确保历史净值计算一致
+                    decimal txAmountInTarget;
+                    if (tx.TotalAmountBase.HasValue && tx.TotalAmountBase > 0)
+                    {
+                        txAmountInTarget = tx.TotalAmountBase.Value;
+                    }
+                    else
+                    {
+                        // 回退到当前汇率（历史数据可能不准确）
+                        txAmountInTarget = await _exchangeRateService.ConvertAmountAsync(
+                            tx.TotalAmount, tx.Currency, targetCurrency);
+                    }
+                    
                     if (holdings.ContainsKey(tx.StockCode))
                     {
                         var existing = holdings[tx.StockCode];
                         decimal newShares = existing.shares + tx.Amount;
-                        decimal newCost = existing.cost + tx.TotalAmount;
-                        holdings[tx.StockCode] = (newShares, newCost, tx.Currency, tx.AssetType);
+                        decimal newCostInTarget = existing.costInTargetCurrency + txAmountInTarget;
+                        holdings[tx.StockCode] = (newShares, newCostInTarget, tx.Currency, tx.AssetType);
                     }
                     else
                     {
-                        holdings[tx.StockCode] = (tx.Amount, tx.TotalAmount, tx.Currency, tx.AssetType);
+                        holdings[tx.StockCode] = (tx.Amount, txAmountInTarget, tx.Currency, tx.AssetType);
                     }
 
-                    // 累计投入成本（转换为目标币种）
-                    decimal txAmountInTarget = await _exchangeRateService.ConvertAmountAsync(
-                        tx.TotalAmount, tx.Currency, targetCurrency);
                     cumulativeCost += txAmountInTarget;
                 }
                 else if (tx.Type == "sell")
@@ -404,7 +429,7 @@ public class PortfolioNavService : IPortfolioNavService
                         
                         decimal soldRatio = tx.Amount / existing.shares;
                         decimal remainingShares = existing.shares - tx.Amount;
-                        decimal remainingCost = existing.cost * (1 - (decimal)soldRatio);
+                        decimal remainingCostInTarget = existing.costInTargetCurrency * (1 - (decimal)soldRatio);
 
                         if (remainingShares <= 0)
                         {
@@ -412,15 +437,15 @@ public class PortfolioNavService : IPortfolioNavService
                         }
                         else
                         {
-                            holdings[tx.StockCode] = (remainingShares, remainingCost, existing.currency, existing.assetType);
+                            holdings[tx.StockCode] = (remainingShares, remainingCostInTarget, existing.currency, existing.assetType);
                         }
 
-                        // 按比例减少累计投入成本（修复：使用该标的的成本，而非全局累计成本）
-                        // 先将该标的的成本转换为目标币种
-                        decimal existingCostInTarget = await _exchangeRateService.ConvertAmountAsync(
-                            existing.cost, existing.currency ?? targetCurrency, targetCurrency);
-                        decimal costToReduce = existingCostInTarget * (decimal)soldRatio;
+                        // 按比例减少累计投入成本（直接用目标币种成本，无需再次汇率转换）
+                        decimal costToReduce = existing.costInTargetCurrency * (decimal)soldRatio;
                         cumulativeCost -= costToReduce;
+                        
+                        _logger.LogDebug("卖出成本计算: {StockCode}, 卖出比例={Ratio}, 减少成本={CostToReduce}, 剩余累计成本={CumulativeCost}",
+                            tx.StockCode, soldRatio.ToString("P2"), costToReduce, cumulativeCost);
                     }
                 }
             }
@@ -433,7 +458,7 @@ public class PortfolioNavService : IPortfolioNavService
             bool hasValidPrice = true;
             List<string> failedSymbols = new List<string>();
             
-            foreach (var (stockCode, (shares, cost, currency, assetType)) in holdings)
+            foreach (var (stockCode, (shares, costInTargetCurrency, currency, assetType)) in holdings)
             {
                 var priceResult = await GetHistoricalPriceAsync(stockCode, assetType ?? "Stock", date);
                 if (priceResult == null || priceResult <= 0)

AssetManager.Services/PortfolioService.cs

@@ -680,6 +680,24 @@ public class PortfolioService : IPortfolioService
             }
         }
 
+        // 获取交易时汇率并保存（用于历史净值计算）
+        string baseCurrency = portfolio.Currency ?? "CNY";
+        decimal? exchangeRate = null;
+        decimal? totalAmountBase = null;
+        
+        if (!string.IsNullOrEmpty(request.Currency) && !request.Currency.Equals(baseCurrency, StringComparison.OrdinalIgnoreCase))
+        {
+            exchangeRate = await _exchangeRateService.GetExchangeRateAsync(request.Currency, baseCurrency);
+            totalAmountBase = (decimal)(request.Price * request.Amount) * exchangeRate.Value;
+            _logger.LogInformation("交易汇率: {FromCurrency} -> {ToCurrency} = {Rate}, 原始金额={Amount}, 本位币金额={BaseAmount}",
+                request.Currency, baseCurrency, exchangeRate, request.Price * request.Amount, totalAmountBase);
+        }
+        else
+        {
+            exchangeRate = 1.0m;
+            totalAmountBase = (decimal)(request.Price * request.Amount);
+        }
+
         var transaction = new Transaction
         {
             Id = "trans-" + Guid.NewGuid().ToString().Substring(0, 8),
@@ -692,6 +710,8 @@ public class PortfolioService : IPortfolioService
             Price = (decimal)request.Price,
             TotalAmount = (decimal)(request.Price * request.Amount),
             Currency = request.Currency,
+            ExchangeRate = exchangeRate,
+            TotalAmountBase = totalAmountBase,
             Status = "completed",
             Remark = request.Remark ?? string.Empty,
             TransactionTime = transactionTime,

sql/migrate_financial_fields.sql

@@ -0,0 +1,43 @@
+-- =============================================
+-- 数据库迁移脚本：为金融计算增加关键字段
+-- 执行前请备份数据
+-- =============================================
+
+-- 1. positions 表添加 total_cost 字段
+ALTER TABLE positions ADD COLUMN total_cost DECIMAL(18,4) DEFAULT 0;
+
+-- 初始化 total_cost（shares * avg_price）
+UPDATE positions SET total_cost = shares * avg_price WHERE total_cost = 0 OR total_cost IS NULL;
+
+-- 验证 positions 更新
+SELECT 'positions' as table_name, COUNT(*) as total, 
+       SUM(CASE WHEN total_cost > 0 THEN 1 ELSE 0 END) as with_cost
+FROM positions;
+
+-- =============================================
+
+-- 2. transactions 表添加汇率相关字段
+ALTER TABLE transactions ADD COLUMN exchange_rate DECIMAL(18,6) DEFAULT NULL;
+ALTER TABLE transactions ADD COLUMN total_amount_base DECIMAL(18,4) DEFAULT NULL;
+
+-- 为已有交易记录填充当前汇率（历史数据只能用当前汇率近似）
+-- 注意：这会导致历史净值计算有汇率偏差，建议手动修正重要历史交易
+-- UPDATE transactions t
+-- JOIN portfolios p ON t.portfolio_id = p.id
+-- SET t.exchange_rate = 1.0, t.total_amount_base = t.total_amount
+-- WHERE t.currency = p.currency OR t.currency IS NULL;
+
+-- 验证 transactions 更新
+SELECT 'transactions' as table_name, COUNT(*) as total,
+       SUM(CASE WHEN total_amount_base IS NOT NULL THEN 1 ELSE 0 END) as with_base_amount
+FROM transactions;
+
+-- =============================================
+
+-- SQLite 版本（如果使用 SQLite）
+-- ALTER TABLE positions ADD COLUMN total_cost REAL DEFAULT 0;
+-- UPDATE positions SET total_cost = shares * avg_price;
+
+-- SQLite 不支持多个 ADD COLUMN，需要分开执行
+-- ALTER TABLE transactions ADD COLUMN exchange_rate REAL DEFAULT NULL;
+-- ALTER TABLE transactions ADD COLUMN total_amount_base REAL DEFAULT NULL;