第C#表達式樹Expression動態創建表達式///typeparamname="T"泛型/typeparam

publicstaticclassExpressionExtensionTwhereT:class,new()

///summary

///表達式動態拼接

////summary

publicstaticExpressionFuncT,boolExpressionSplice(ListQueryEntityentities)

if(entities.Count1)

returnex=true;

varexpression_first=CreateExpressionDelegate(entities[0]);

foreach(varentityinentities.Skip(1))

varexpression=CreateExpressionDelegate(entity);

InvocationExpressioninvocation=Expression.Invoke(expression_first,expression.Parameters.CastExpression

BinaryExpressionbinary;

//邏輯運算符判斷

if(entity.LogicalOperator.ToUpper().Equals("OR"))

binary=Expression.Or(expression.Body,invocation);

else

binary=Expression.And(expression.Body,invocation);

expression_first=Expression.LambdaFuncT,bool(binary,expression.Parameters);

returnexpression_first;

///summary

///創建ExpressionTDelegate

////summary

privatestaticExpressionFuncT,boolCreateExpressionDelegate(QueryEntityentity)

ParameterExpressionparam=Expression.Parameter(typeof(T));

Expressionkey=param;

varentityKey=entity.Key.Trim();

//包含'.'，說明是父表的字段

if(entityKey.Contains('.'))

vartableNameAndField=entityKey.Split('.');

key=Expression.Property(key,tableNameAndField[0].ToString());

key=Expression.Property(key,tableNameAndField[1].ToString());

else

key=Expression.Property(key,entityKey);

Expressionvalue=Expression.Constant(ParseType(entity));

Expressionbody=CreateExpression(key,value,entity.Operator);

varlambda=Expression.LambdaFuncT,bool(body,param);

returnlambda;

///summary

///屬性類型轉換

////summary

///paramname="entity"查詢實體/param

///returns/returns

privatestaticobjectParseType(QueryEntityentity)

PropertyInfoproperty;

//包含'.'，說明是子類的字段

if(entity.Key.Contains('.'))

vartableNameAndField=entity.Key.Split('.');

property=typeof(T).GetProperty(tableNameAndField[0],BindingFlags.IgnoreCase|BindingFlags.Public|BindingFlags.Instance);

property=property.PropertyType.GetProperty(tableNameAndField[1],BindingFlags.IgnoreCase|BindingFlags.Public|BindingFlags.Instance);

else

property=typeof(T).GetProperty(entity.Key,BindingFlags.IgnoreCase|BindingFlags.Public|BindingFlags.Instance);

returnConvert.ChangeType(entity.Value,property.PropertyType);

catch(Exception)

thrownewArgumentException("字段類型轉換失敗：字段名錯誤或值類型不正確");

///summary

///創建Expression

////summary

privatestaticExpressionCreateExpression(Expressionleft,Expressionvalue,stringentityOperator)

if(!Enum.TryParse(entityOperator,true,outOperatorEnumoperatorEnum))

thrownewArgumentException("操作方法不存在,請檢查operator的值");

returnoperatorEnumswitch

OperatorEnum.Equals=Expression.Equal(left,Expression.Convert(value,left.Type)),

OperatorEnum.NotEqual=Expression.NotEqual(left,Expression.Convert(value,left.Type)),

OperatorEnum.Contains=Expression.Call(left,typeof(string).GetMethod("Contains",newType[]{typeof(string)}),value),

OperatorEnum.StartsWith=Expression.Call(left,typeof(string).GetMethod("StartsWith",newType[]{typeof(string)}),value),

OperatorEnum.EndsWith=Expression.Call(left,typeof(string).GetMethod("EndsWith",newType[]{typeof(string)}),value),

OperatorEnum.Greater=Expression.GreaterThan(left,Expression.Convert(value,left.Type)),

OperatorEnum.GreaterEqual=Expression.GreaterThanOrEqual(left,Expression.Convert(value,left.Type)),

OperatorEnum.Less=Expression.LessThan(left,Expression.Convert(value,left.Type)),

OperatorEnum.LessEqual=Expression.LessThanOrEqual(left,Expression.Convert(value,left.Type)),

_=Expression.Equal(left,Expression.Convert(value,left.Type)),

}

使用示例

例如有以下兩個實體類，Address是User的子類

publicclassUser

publicintId{get;set;}

publicstringName{get;set;}=string.Empty;

publicintAge{get;set;}

publicDateTimeCreateTime{get;set;}

publicAddressAddress{get;set;}

publicclassAddress

publicstringProvince{get;set;}

publicstringCity{get;set;}

}

單條件查詢

查詢用戶表中名稱(name)包含"chen"：

ListQueryEntitylist=newListQueryEntity

newQueryEntity

Key="name",

Value="chen",

Operator="Contains"

varexpression=ExpressionExtensionUser.ExpressionSplice(list);

//expression=Param_0=Param_0.Name.Contains("chen")

查詢用戶表中年齡(age)大于等于18：

ListQueryEntitylist=newListQueryEntity

newQueryEntity

Key="age",

Value="18",

Operator="GreaterEqual"

varexpression=ExpressionExtensionUser.ExpressionSplice(list);

//expression=Param_0=Param_0.Name.GreaterThanOrEqual(18)

多條件查詢

查詢用戶表中名稱(name)包含"chen"并且年齡(age)大于等于18：

ListQueryEntitylist=newListQueryEntity

newQueryEntity

Key="name",

Value="chen",

Operator="Contains"

newQueryEntity

Key="age",

Value="18",

Operator="GreaterEqual",

//注意：這里得填入"AND",代表兩個條件是并且的關系，如果需要查詢名稱包含"chen"或者年齡大于等于18，則填入"OR"

"logicalOperator":"AND"

varexpression=ExpressionExtensionUser.ExpressionSplice(list);

//expression=Param_0=((Param_0.Status=Convert(1,Int32))AndInvoke(Param_1=Param_1.OpenId.Contains("9JJdFTVt6oimCgdbW61sk"),Param_0))

多表查詢

查詢用戶表中名稱(name)包含"chen"并且地址(address)在廣東省