动态Lambda表达式-选择一个子属性

如何解决动态Lambda表达式-选择一个子属性

我尝试生成Lambda表达式以选择日期属性和值属性，以在客户端生成图形。

我想出了以下代码-选择Value Property

可以正常工作

void Main()
{
    // key to be selected by end user - to view values of it by datetime
    var inputKey = nameof(VehicleSensorLog.iTemperatureSensor1);
    
    // always need datetime for graph
    var dateKey = nameof(VehicleSensorLog.VehicleMonitoringLog.dtUTCDateTime);

    Type gType = typeof(GraphDTO);
    Type inputType = typeof(VehicleSensorLog);

    ParameterExpression xParam = Expression.Parameter(inputType,"g");

    // new statement "new GraphDTO()"
    var xNew = Expression.New(gType);

    // select properties
    var xPropValue = gType.GetProperty(nameof(GraphDTO.Value));
    var xSourceValue = Expression.Property(xParam,inputType.GetProperty(inputKey));
    var xPropDateTime = gType.GetProperty(nameof(GraphDTO.LogDateTime));

    // HOW TO DO THIS?
    // -----------------
    var xSourcePropDateTime = Expression.PropertyOrField(xParam,"VehicleMonitoringLog.dtUTCDateTime");

    // Bind / Map from Origional to New GraphDTO property (set value "Field1 = o.Field1")
    var xBindExpression = Expression.Bind(xPropValue,xSourceValue);
    var xBindExpressionDateTime = Expression.Bind(xPropDateTime,xSourceValue);

    // initialization "new Data { Field1 = o.Field1,Field2 = o.Field2 }"
    var xInit = Expression.MemberInit(xNew,new List<MemberAssignment>() { xBindExpression,xBindExpressionDateTime });

    // expression "o => new Data { Field1 = o.Field1,Field2 = o.Field2 }"
    var lambda = Expression.Lambda<Func<VehicleSensorLog,GraphDTO>>(xInit,xParam);

    // finally select the logs based on lambda created
    this.VehicleSensorLogs.Select(lambda).Take(10).Dump();

}

public class GraphDTO
{
    public DateTime LogDateTime { get; set; }
    public Double? Value { get; set; }
}

我无法从源中选择DateTime属性，因为它是导航（子）属性。我尝试了以下两种方法：

var xSourcePropDateTime = Expression.PropertyOrField(xParam,"VehicleMonitoringLog.dtUTCDateTime");



var xSourcePropDateTime = Expression.Property(xParam,inputType.GetProperty("VehicleMonitoringLog.dtUTCDateTime"));

如何为子属性创建表达式？

解决方法

PropertyOrField方法不支持用于访问嵌套属性的点表示法，因此您需要像这样连续获取属性：

import (
   "gorm.io/gorm"
   "gorm.io/driver/mysql"
)


func main(){
    db,err := gorm.Open(mysql.Open(MYSQL_CONNECTION_STRING),&gorm.Config{})

    if err != nil {
        fmt.Println(err.Error())
    }else{
        db.Clauses(clause.Insert{Modifier: "IGNORE"}).Create(&user)
    }
}