环境:Visual Studio2008 .NET Framework3.5
场合:查询条件不确定,需动态生成
动态构造代码:
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/**//// <summary>
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/// 动态构造Lambda表达式
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/// </summary>
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/// <typeparam name="T">查询目标实体</typeparam> 5
public class ConstructLambda<T> where T : class, new()
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{
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private Type TType;
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/**//// <summary>
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/// 构造方法
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/// </summary>
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public ConstructLambda()
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{
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TType = typeof(T);
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}
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/**//// <summary>
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/// 构造与表达式
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/// </summary>
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/// <param name="dictionary">构造源</param>
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/// <returns>lambda表达式</returns>
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public Expression<Func<T, bool>> GetAndLambdaExpression(Dictionary<string, string> dictionary)
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{
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Expression expression_return = Expression.Constant(true);
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ParameterExpression expression_param = Expression.Parameter(TType, "p");
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foreach (string key in dictionary.Keys)
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{
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Expression temp = Expression.Equal(Expression.Call(Expression.Property(expression_param, TType.GetProperty(key)), TType.GetMethod("ToString")),
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Expression.Constant(dictionary[key]));
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expression_return = Expression.And(expression_return, temp);
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}
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return (Expression<Func<T, bool>>)Expression.Lambda<Func<T, bool>>(expression_return, new ParameterExpression[]
{ expression_param });
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}
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/**//// <summary>
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/// 构造或表达式
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/// </summary>
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/// <param name="dictionary">构造源</param>
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/// <returns>Lambda表达式</returns>
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public Expression<Func<T, bool>> GetOrLambdaExpression(Dictionary<string, string> dictionary)
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{
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Expression expression_return = Expression.Constant(false);
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ParameterExpression expression_param = Expression.Parameter(TType, "p");
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foreach (string key in dictionary.Keys)
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{
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Expression temp = Expression.Equal(Expression.Call(Expression.Property(expression_param, TType.GetProperty(key)), TType.GetMethod("ToString")),
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Expression.Constant(dictionary[key]));
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expression_return = Expression.Or(expression_return, temp);
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}
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return (Expression<Func<T, bool>>)Expression.Lambda<Func<T, bool>>(expression_return, new ParameterExpression[]
{ expression_param });
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}50![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
实例:
测试数据:
虚拟实体:
public class Person
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public string Name
{ get; set; }
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public string Sex
{ get; set; }
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public int Age
{ get; set; }
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
public DateTime Birthday
{ get; set; }
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public Person()
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{ }
}
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虚拟查找源:
private Dictionary<string, string> dictionary = new Dictionary<string, string>()
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
{
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{"Name","JT"},
{"Sex","男"},
{"Age","20"},
{"Birthday","02/02/2008"}
};
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
1,无条件查找:
new ConstructLambda<Person>().GetAndLambdaExpression(new Dictionary<string, string>()).ToString()返回结果:
p => True
new ConstructLambda<Person>().GetOrLambdaExpression(new Dictionary<string, string>()).ToString()返回结果:
p => False
2,多条件查找:
new ConstructLambda<Person>().GetAndLambdaExpression(dictionary).ToString()返回结果:
p => ((((True And (p.Name.ToString() = "JT")) And (p.Sex.ToString() = "男")) And (p.Age.ToString() = "20")) And (p.Birthday.ToString() = "02/02/2008"))
new ConstructLambda<Person>().GetOrLambdaExpression(dictionary).ToString()返回结果:
p => ((((False Or (p.Name.ToString() = "JT")) Or (p.Sex.ToString() = "男")) Or (p.Age.ToString() = "20")) Or (p.Birthday.ToString() = "02/02/2008"))