public override LambdaExpression GetBindExpression()
{
bool sourceIsQueryable = SourceValueType.IsGenericQueryable();
bool targetIsQueryable = TargetValueType.IsGenericQueryable();
var selectMethod = sourceIsQueryable ? MethodFinder.GetQuerybleSelect <TSourceValueItem, TTargetValueItem>() : MethodFinder.GetEnumerableSelect <TSourceValueItem, TTargetValueItem>();
var callSelectExpression = Expression.Call(selectMethod, this.SourceExpression.Body, GetAssignExpression());
var toResultExpression = GetResultExpression(callSelectExpression, sourceIsQueryable, targetIsQueryable);
// 需要处理source为null的情况
var resultExpression = Expression.Condition(
Expression.Equal(this.SourceExpression.Body, Expression.Constant(null))
, Expression.Constant(null, this.TargetValueType), toResultExpression);
return(Expression.Lambda(resultExpression, this.SourceExpression.Parameters.First()));
}
private Expression GetResultExpression(Expression selectExpression, bool sourceIsQueryable, bool targetIsQueryable)
{
if (sourceIsQueryable && targetIsQueryable)
{
return(selectExpression);
}
if (!sourceIsQueryable && targetIsQueryable)
{
return(Expression.Call(
MethodFinder.GetAsQueryable(TargetValueType.GetQueryableItemType()),
selectExpression));
}
var toResultMethod = this.TargetValueType.IsArray ? MethodFinder.GetEnumerableToArray <TTargetValueItem>() : MethodFinder.GetEnumerableToList <TTargetValueItem>();
return(Expression.Call(toResultMethod, selectExpression));
}
