记录Linq中lambda动态表达式的使用方式

项目中有的时候我们会用到动态表达式的方式去查询数据，这里简单记录下个人的使用方式，方便使用↓

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 //构建参数表达式
 ParameterExpression parameter = Expression.Parameter(typeof(SimpleResult));
 Expression conditionValue = Expression.Equal(Expression.Property(parameter, groupFileName), Expression.Constant(value, typeof(Object)));
 var lambdaValue = Expression.Lambda<Func<SimpleResult, bool>>(
    conditionValue,
    parameter);
 var groupCount = resultData.AsQueryable().Count(lambdaValue);
 var item = new GroupModel { GroupName = groupFileName, GroupValue = value?.ToString(), GroupCount = groupCount };
 listObj.Add(item);

 /*

  1、创建表达式
  2、创建表达式参数
  3、查询

  */

 // 表达式传过去的参数
 // ParameterExpression parameter1 = Expression.Parameter(typeof(SimpleResult), "o");
 // 使用的字段
 //MemberExpression member1 = Expression.PropertyOrField(parameter1, groupFileName);
 // 要比较的值
 //ConstantExpression constant1 = Expression.Constant(value, typeof(Object));
 // query
 //var query = Expression.Equal(member1, constant1);//Equal等于；GreaterThanOrEqual大于；LessThanOrEqual小于

 // var lambda = Expression.Lambda<Func<SimpleResult, bool>>(query, parameter1);

 // var groupCount2 = resultData.AsQueryable().Count(lambda);

还有另外一种动态表达式的使用方式，通过安装DynamicExpresso.CoreNuget包

参考地址：https://github.com/davideicardi/DynamicExpresso

 ==============================（Install - Package DynamicExpresso.Core）======================================

 var whereExpression = $"m.{queryField}==\"{queryValue}\"";

 string whereExpression = "customer.Age > 18 && customer.Gender == 'F'";

 var interpreter = new Interpreter();
 Func<Customer, bool> dynamicWhere = interpreter.ParseAsDelegate<Func<Customer, bool>>(whereExpression, "customer");

 Assert.AreEqual(, customers.Where(dynamicWhere).Count());

 =====================================================================================================
 string whereExpression = "customer.Age > 18 && customer.Gender == 'F'";

 var interpreter = new Interpreter();
 Expression<Func<Customer, bool>> expression = interpreter.ParseAsExpression<Func<Customer, bool>>(whereExpression, "customer");

 Assert.AreEqual(, customers.Where(expression).Count());

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