C#表達(dá)式樹Expression動態(tài)創(chuàng)建表達(dá)式
上一篇中說到了 Expression 的一些概念性東西,其實也是為了這一篇做知識準(zhǔn)備。為了實現(xiàn) EFCore 的多條件、連表查詢,簡化查詢代碼編寫,也就有了這篇文章。
在一些管理后臺中,對數(shù)據(jù)進(jìn)行多條件查詢是一件很普遍的事情,比如在用戶列表需要實現(xiàn)可以對 "用戶名"、"手機(jī)號"、"賬戶是否凍結(jié)" 等等一系列的條件查詢,常見的處理方式就是通過一系列 if...else... 來對條件進(jìn)行拼接。這會導(dǎo)致查詢接口實現(xiàn)起來堆疊了一堆看起來有用但實際很繁瑣的代碼。所以根據(jù)前后端請求報文協(xié)商,我們就可以按照一定的格式來動態(tài)創(chuàng)建表達(dá)式樹。
創(chuàng)建 QueryEntity 類
QueryEntity 是前端向 API 傳遞的參數(shù)列表,通過這個類,服務(wù)端可以知道前端需要查詢哪個字段,使用什么方法(Equals、Contains)過濾。
/// <summary> /// 查詢實體 /// </summary> public class QueryEntity { /// <summary> /// 字段名稱 /// </summary> public string Key { get; set; } /// <summary> /// 值 /// </summary> public string Value { get; set; } /// <summary> /// 操作方法,對應(yīng)OperatorEnum枚舉類 /// </summary> public string Operator { get; set; } /// <summary> /// 邏輯運算符,只支持AND、OR /// </summary> public string LogicalOperator { get; set; } }
創(chuàng)建 OperatorEnum 類
OperatorEnum 這是一個操作方法的枚舉類,規(guī)定了 API 允許的查詢方法,比如 Equals、Contains 等等。
/// <summary> /// 操作方法枚舉 /// </summary> public enum OperatorEnum { /// <summary> /// 等于 /// </summary> Equals, /// <summary> /// 不等于 /// </summary> NotEqual, /// <summary> /// 包含 /// </summary> Contains, /// <summary> /// 由什么開始 /// </summary> StartsWith, /// <summary> /// 由什么結(jié)束 /// </summary> EndsWith, /// <summary> /// 大于 /// </summary> Greater, /// <summary> /// 大于等于 /// </summary> GreaterEqual, /// <summary> /// 小于 /// </summary> Less, /// <summary> /// 小于等于 /// </summary> LessEqual, }
創(chuàng)建 ExpressionExtension 類
ExpressionExtension 類實現(xiàn)了表達(dá)式樹的動態(tài)創(chuàng)建,將前端傳入的多條件查詢轉(zhuǎn)換成表達(dá)式,用于 EFCore 的查詢。
/// <summary> /// 表達(dá)式擴(kuò)展 /// </summary> /// <typeparam name="T">泛型</typeparam> public static class ExpressionExtension<T> where T : class, new() { /// <summary> /// 表達(dá)式動態(tài)拼接 /// </summary> public static Expression<Func<T, bool>> ExpressionSplice(List<QueryEntity> entities) { if (entities.Count < 1) { return ex => true; } var expression_first = CreateExpressionDelegate(entities[0]); foreach (var entity in entities.Skip(1)) { var expression = CreateExpressionDelegate(entity); InvocationExpression invocation = Expression.Invoke(expression_first, expression.Parameters.Cast<Expression>()); BinaryExpression binary; // 邏輯運算符判斷 if (entity.LogicalOperator.ToUpper().Equals("OR")) { binary = Expression.Or(expression.Body, invocation); } else { binary = Expression.And(expression.Body, invocation); } expression_first = Expression.Lambda<Func<T, bool>>(binary, expression.Parameters); } return expression_first; } /// <summary> /// 創(chuàng)建 Expression<TDelegate> /// </summary> private static Expression<Func<T, bool>> CreateExpressionDelegate(QueryEntity entity) { ParameterExpression param = Expression.Parameter(typeof(T)); Expression key = param; var entityKey = entity.Key.Trim(); // 包含'.',說明是父表的字段 if (entityKey.Contains('.')) { var tableNameAndField = entityKey.Split('.'); key = Expression.Property(key, tableNameAndField[0].ToString()); key = Expression.Property(key, tableNameAndField[1].ToString()); } else { key = Expression.Property(key, entityKey); } Expression value = Expression.Constant(ParseType(entity)); Expression body = CreateExpression(key, value, entity.Operator); var lambda = Expression.Lambda<Func<T, bool>>(body, param); return lambda; } /// <summary> /// 屬性類型轉(zhuǎn)換 /// </summary> /// <param name="entity">查詢實體</param> /// <returns></returns> private static object ParseType(QueryEntity entity) { try { PropertyInfo property; // 包含'.',說明是子類的字段 if (entity.Key.Contains('.')) { var tableNameAndField = entity.Key.Split('.'); property = typeof(T).GetProperty(tableNameAndField[0], BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance); property = property.PropertyType.GetProperty(tableNameAndField[1], BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance); } else { property = typeof(T).GetProperty(entity.Key, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance); } return Convert.ChangeType(entity.Value, property.PropertyType); } catch (Exception) { throw new ArgumentException("字段類型轉(zhuǎn)換失?。鹤侄蚊e誤或值類型不正確"); } } /// <summary> /// 創(chuàng)建 Expression /// </summary> private static Expression CreateExpression(Expression left, Expression value, string entityOperator) { if (!Enum.TryParse(entityOperator, true, out OperatorEnum operatorEnum)) { throw new ArgumentException("操作方法不存在,請檢查operator的值"); } return operatorEnum switch { OperatorEnum.Equals => Expression.Equal(left, Expression.Convert(value, left.Type)), OperatorEnum.NotEqual => Expression.NotEqual(left, Expression.Convert(value, left.Type)), OperatorEnum.Contains => Expression.Call(left, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), value), OperatorEnum.StartsWith => Expression.Call(left, typeof(string).GetMethod("StartsWith", new Type[] { typeof(string) }), value), OperatorEnum.EndsWith => Expression.Call(left, typeof(string).GetMethod("EndsWith", new Type[] { typeof(string) }), value), OperatorEnum.Greater => Expression.GreaterThan(left, Expression.Convert(value, left.Type)), OperatorEnum.GreaterEqual => Expression.GreaterThanOrEqual(left, Expression.Convert(value, left.Type)), OperatorEnum.Less => Expression.LessThan(left, Expression.Convert(value, left.Type)), OperatorEnum.LessEqual => Expression.LessThanOrEqual(left, Expression.Convert(value, left.Type)), _ => Expression.Equal(left, Expression.Convert(value, left.Type)), }; } }
使用示例
例如有以下兩個實體類,Address 是 User 的子類
public class User { public int Id { get; set; } public string Name { get; set; } = string.Empty; public int Age { get; set; } public DateTime CreateTime { get; set; } public Address Address { get; set; } } public class Address { public string Province { get; set; } public string City { get; set; } }
單條件查詢
查詢用戶表中名稱(name) 包含 "chen" :
List<QueryEntity> list = new List<QueryEntity> { new QueryEntity { Key = "name", Value = "chen", Operator = "Contains" } }; var expression = ExpressionExtension<User>.ExpressionSplice(list); // expression = Param_0 => Param_0.Name.Contains("chen")
查詢用戶表中年齡(age) 大于等于 18:
List<QueryEntity> list = new List<QueryEntity> { new QueryEntity { Key = "age", Value = "18", Operator = "GreaterEqual" } }; var expression = ExpressionExtension<User>.ExpressionSplice(list); // expression = Param_0 => Param_0.Name.GreaterThanOrEqual(18)
多條件查詢
查詢用戶表中名稱(name) 包含 "chen" 并且年齡(age) 大于等于 18:
List<QueryEntity> list = new List<QueryEntity> { new QueryEntity { Key = "name", Value = "chen", Operator = "Contains" }, new QueryEntity { Key = "age", Value = "18", Operator = "GreaterEqual", // 注意:這里得填入 "AND",代表兩個條件是并且的關(guān)系,如果需要查詢名稱包含 "chen" 或者 年齡大于等于18,則填入 "OR" "logicalOperator": "AND" } }; var expression = ExpressionExtension<User>.ExpressionSplice(list); // expression = Param_0 => ((Param_0.Status >= Convert(1, Int32)) And Invoke(Param_1 => Param_1.OpenId.Contains("9JJdFTVt6oimCgdbW61sk"), Param_0))
多表查詢
查詢用戶表中名稱(name) 包含 "chen" 并且 地址(address)在廣東?。?/p>
List<QueryEntity> list = new List<QueryEntity> { new QueryEntity { Key = "name", Value = "chen", Operator = "Contains" }, new QueryEntity { Key = "address.Province", Value = "廣東省", Operator = "Equals", // 注意:這里得填入 "AND",代表兩個條件是并且的關(guān)系,如果需要查詢名稱包含 "chen" 或者 年齡大于等于18,則填入 "OR" "logicalOperator": "AND" } }; var expression = ExpressionExtension<BookingRecord>.ExpressionSplice(list); // expression = {Param_0 => ((Param_0.Address.Province == Convert("廣東省", String)) And Invoke(Param_1 => Param_1.Name.Contains("chen"), Param_0))}
到此這篇關(guān)于C#表達(dá)式樹Expression動態(tài)創(chuàng)建表達(dá)式的文章就介紹到這了。希望對大家的學(xué)習(xí)有所幫助,也希望大家多多支持腳本之家。
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