Dynamic construction of lambda expressions

Environment: Visual Studio2008. NET Framework3.5

Situation: Query condition is uncertain, it needs to be generated dynamically

Dynamic Construction Code:

1/**////<summary>


2///Dynamic construction of lambda expressions


3///</summary>


4///<typeparam name= "T" > Query target entity </typeparam>


5 public class constructlambda<t> where T:class, new ()


6 {


7 private Type ttype;


8/**////<summary>


9///Construction Method


///</summary>


public Constructlambda ()


12 {


ttype = typeof (T);


14}


/**////<summary>


16///structure and expression


///</summary>


///<param name= "dictionary" > Tectonic source </param>


///<RETURNS>LAMBDA expression </returns>


public expression<func<t, bool>> getandlambdaexpression (dictionary<string, string> dicti Onary)


21 {


Expression Expression_return = Expression.constant (true);


parameterexpression Expression_param = Expression.parameter (Ttype, "P");


foreach (String key in dictionary. Keys)


25 {


Expression temp = expression.equal (Expression.call expression.property (Expression_param, Ttype.get Property (key)), Ttype.getmethod ("ToString"),


expression.constant (Dictionary[key]));


Expression_return = Expression.and (Expression_return, temp);


29}


Return (expression<func<t, bool>>) expression.lambda<func<t, bool>> (Expression_return , new parameterexpression[] {expression_param});


31}


32


/**////<summary>


34///construction or expression


///</summary>


///<param name= "dictionary" > Tectonic source </param>


Notoginseng///<returns>lambda expression </returns>


public expression<func<t, bool>> getorlambdaexpression (dictionary<string, string> dictio nary)


39 {


Expression Expression_return = Expression.constant (false);


parameterexpression Expression_param = Expression.parameter (Ttype, "P");


foreach (String key in dictionary. Keys)


43 {


Expression temp = expression.equal (Expression.call expression.property (Expression_param, Ttype.getproper Ty (key)), Ttype.getmethod ("ToString"),


expression.constant (Dictionary[key]);


Expression_return = expression.or (Expression_return, temp);


47}


(expression<func<t, bool>>) expression.lambda<func<t, bool>> (Expression_ Return, new parameterexpression[] {expression_param});


49}


50