生成LinqToEntities其中声明取决于用户选择 [英] Generating LinqToEntities Where statement depending on the user selection

问题描述

我有用户界面，用户可以选择该列的网格列（如年龄）和运算符（小于，等于或大于）。

网格数据然后根据选择进行过滤。

我有一个从客户端的JSON中反序列化的类。

  ///< summary> 
 ///用于减少网格结果的过滤器
 ///< / summary> 
 public class Filter 
 {
 ///< summary> 
 ///列名称
 ///< / summary> 
 public string name; 
 
公共字符串值; 
 
 public int @operator {private get;组; 
 
 public Operator Operator（）
 {
 return（Operator）@operator; 
} 
} 
 
 public enum运算符
 {
无= -1，
 LesserThan = 0，
等于= 1 ，
 GreaterThan = 2 
} 
  

由于自然动态添加新列为了过滤我想创建访问数据的通用解决方案。

我想避免有大量if / switch语句，如

$



{
if（operator == Operator.LesserThan ）
{
query = entities.Where（o => o.Age< age）;
}
else if（operator == Operator.GreaterThan）
{
query = entities.Where（o => o.Age> age）;
}
等

break;
}
等
}

任何想法如何创建更为通用的解决方案？

更新
似乎有很多方法可以实现比十亿if语句更清晰的解决方案。现在我只需要比较不同的解决方案。

解决方案

你可以使用动态LINQ 创建查询动态

编辑：

动态LINQ查询的示例如下所示，假设列名称网格与实体中的字段名称相同：

  string queryString; 
 queryString = columnName; 
 if（operator == Operator.LesserThan）
 {
 queryString + =<; 
} 
 else if（operator == Operator.GreaterThan）
 {
 queryString + =>; 
} 
等
 queryString + = age.ToString（）; //或使用绑定变量，没有尝试自己在动态LINQ 
 
 query = intites.Where（queryString）; 
  

I have user-interface where user can select grid column (like age) and operator (lesser than, equals or greater than) for that column.

Grid data is then filtered according to the selection.

I have a following classes that are deserialized from the JSON that is coming from the client.

/// <summary>
/// Filter for reducing grid results
/// </summary>
public class Filter
{
    /// <summary>
    /// Name of the column
    /// </summary>
    public string name;

    public string value;

    public int @operator { private get; set; }

    public Operator Operator()
    {
        return (Operator) @operator;
    }
}

public enum Operator
{
    None = -1,
    LesserThan = 0,
    Equals = 1,
    GreaterThan = 2
}

Due to the nature dynamically adding new columns for filtering I would like to create generic solution for accessing the data.

I would like avoid having huge amount if/switch statements like

switch(columnName)
{
    case "age":
    {
        if(operator == Operator.LesserThan)
        {
             query = entities.Where(o => o.Age < age);
        }
        else if (operator == Operator.GreaterThan)
        {
             query = entities.Where(o => o.Age > age);
        }
        etc.

        break;
    }
    etc.
}

Any ideas how to create more generic solution for the problem?

Update It seems that there many ways to accomplish cleaner solution than one billion if statements. Now I just need to compare different solutions.

解决方案

You could use Dynamic LINQ to create the query dynamically

Edit:

An example for Dynamic LINQ query would look like this, assuming that the column names in the grid are the same as the field names in the entity:

string queryString;
queryString = columnName;
if(operator == Operator.LesserThan)
{
  queryString += " < ";
}
else if (operator == Operator.GreaterThan)
{
  queryString += " > ";
}
etc.
queryString += age.ToString();  // Or use bind variables, haven't tried that myself in dynamic LINQ

query = entites.Where(queryString);

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