/// <summary>
/// 获得Like的表达式
/// </summary>
private static Expression GetLikeExpression(ParameterExpression entityTypeParam, string fieldName, string value)
{
var body = GetEntityAttrExp(entityTypeParam, fieldName, value == null);
var constant = LambdaExpression.Constant(value, typeof(string));
return(Expression.Call(body, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), constant));
}
/// <summary>
/// Costrói uma expressão que actua sobre o objecto.
/// </summary>
/// <param name="pattern">O filtro de pesquisa.</param>
/// <returns>A expressão resultante.</returns>
public Expression <Func <ObjectType, bool> > BuildExpressionTree(string pattern)
{
var patternReader = this.GetPatternReader(pattern);
var stateMachine = new StateMachine <string, ELambdaExpressionWordType>(
this.stateList[0],
this.stateList[1]);
stateMachine.RunMachine(patternReader);
if (this.expressionStack.Count == 0)
{
// Retorna a expressão vazia
var parameterExpression = LambdaExpression.Parameter(
typeof(ObjectType));
var body = LambdaExpression.Constant(true);
var result = LambdaExpression.Lambda <Func <ObjectType, bool> >(
body,
new[] { parameterExpression });
return(result);
}
else
{
var top = this.expressionStack.Pop();
var parameterExpression = LambdaExpression.Parameter(
typeof(ObjectType));
var result = LambdaExpression.Lambda <Func <ObjectType, bool> >(
top,
new[] { parameterExpression });
return(result);
}
}
/// <summary>
/// 根据表达式属性类型 获得 常量表达式
/// </summary>
/// <param name="value"></param>
/// <param name="valueType"></param>
/// <returns></returns>
private static ConstantExpression GetConstExp(object value, Type valueType)
{
if (valueType == value.GetType())
{
return LambdaExpression.Constant(value, valueType);
}
try
{
//把常量转化成相对应的字段属性类型
object newObj = Convert.ChangeType(value, valueType);
return LambdaExpression.Constant(newObj, valueType);
}
catch
{
return LambdaExpression.Constant(value, valueType);
}
}
/// <summary>
/// 获得NotEquel的表达式
/// </summary>
private static Expression GetNotEquelExpression(ParameterExpression entityTypeParam, string fieldName, string rightFieldName, object value)
{
//查询是否 join条件查询
if (!string.IsNullOrEmpty(rightFieldName))
{
var fieldExp = GetEntityAttrExp(entityTypeParam, fieldName, false);
var joinFieldExp = GetEntityAttrExp(entityTypeParam, rightFieldName, false);
return Expression.NotEqual(fieldExp, joinFieldExp);
}
var body = GetEntityAttrExp(entityTypeParam, fieldName, value == null);
//排除空值情况
if (value == null)
{
return Expression.NotEqual(body, LambdaExpression.Constant(null));
}
var constant = GetConstExp(value, body.Type);
return Expression.NotEqual(body, constant);
}
/// <summary>
/// 根据表达式属性类型 获得 常量表达式
/// </summary>
/// <param name="value"></param>
/// <param name="valueType"></param>
/// <returns></returns>
private static ConstantExpression GetConstExp(object value, Type valueType)
{
if (valueType == value.GetType())
{
return(LambdaExpression.Constant(value, valueType));
}
try
{
if (valueType.IsEnum)
{
value = Enum.Parse(valueType, value.ToString());
}
//把常量转化成相对应的字段属性类型
object newObj = Convert.ChangeType(value, valueType);
return(LambdaExpression.Constant(newObj, valueType));
}
catch
{
return(LambdaExpression.Constant(value, valueType));
}
}