public static Expression <TDelegate> ComposePredicate <TDelegate>(List <LambdaExpression> filterPredicates, Expression[] expressionSubstitutes, ParameterExpression parameter)
{
Expression predicateBody = null;
foreach (LambdaExpression filterPredicate in filterPredicates)
{
var body = JoinQueryParameterExpressionReplacer.Replace(filterPredicate, expressionSubstitutes, parameter).Body;
if (predicateBody == null)
{
predicateBody = body;
}
else
{
predicateBody = Expression.AndAlso(predicateBody, body);
}
}
Expression <TDelegate> predicate = Expression.Lambda <TDelegate>(predicateBody, parameter);
return(predicate);
}
public IQuery <TResult> Select <TResult>(Expression <Func <T1, T2, TResult> > selector)
{
if (this._filterPredicates.Count == 0)
{
JoinQueryExpression e1 = new JoinQueryExpression(typeof(TResult), this._rootQuery.QueryExpression, this._joinedQueries, selector);
return(new Query <TResult>(this.DbContext, e1, this._rootQuery.TrackEntity));
}
/*
* q.LeftJoin<City>((user, city) => user.CityId == city.Id).Where((user, city) => user.Name == "lu").Select((user, city) => new { user, city })
* 转换成：
* q.LeftJoin<City>((user, city) => user.CityId == city.Id)
* .Select((user, city) => new JoinResult<T1, T2>() { Item1 = user, Item2 = city })
* .Where(a => a.Item1.Name == "lu")
* .Select(a => new { user = a.user, city = a.city })
*/
Type joinResultType = typeof(JoinResult <T1, T2>);
Expression <Func <T1, T2, JoinResult <T1, T2> > > joinResultSelector = (t1, t2) => new JoinResult <T1, T2>()
{
Item1 = t1, Item2 = t2
};
JoinQueryExpression e = new JoinQueryExpression(joinResultType, this._rootQuery.QueryExpression, this._joinedQueries, joinResultSelector);
IQuery <JoinResult <T1, T2> > q = new Query <JoinResult <T1, T2> >(this.DbContext, e, this._rootQuery.TrackEntity);
ParameterExpression parameter = Expression.Parameter(joinResultType, "a");
Expression[] expressionSubstitutes = QueryHelper.MakeExpressionSubstitutes(joinResultType, parameter);
Expression <Func <JoinResult <T1, T2>, bool> > predicate = QueryHelper.ComposePredicate <Func <JoinResult <T1, T2>, bool> >(this._filterPredicates, expressionSubstitutes, parameter);
var q1 = q.Where(predicate);
Expression <Func <JoinResult <T1, T2>, TResult> > selector2 = JoinQueryParameterExpressionReplacer.Replace(selector, expressionSubstitutes, parameter) as Expression <Func <JoinResult <T1, T2>, TResult> >;
var ret = q1.Select(selector2);
return(ret);
}