public virtual Expression VisitRowNumber(RowNumberExpression rowNumberExpression)
{
Check.NotNull(rowNumberExpression, nameof(rowNumberExpression));
Sql.Append("ROW_NUMBER() OVER(");
GenerateOrderBy(rowNumberExpression.Orderings);
Sql.Append(") AS ").Append(SqlGenerator.DelimitIdentifier(rowNumberExpression.ColumnExpression.Name));
return rowNumberExpression;
}
private Expression VisitSelectExpression(SelectExpression selectExpression)
{
base.Visit(selectExpression);
if (!RequiresRowNumberPaging(selectExpression))
{
return selectExpression;
}
var subQuery = selectExpression.PushDownSubquery();
foreach (var projection in subQuery.Projection)
{
var alias = projection as AliasExpression;
var column = projection as ColumnExpression;
if (column != null)
{
column = new ColumnExpression(column.Name, column.Property, subQuery);
selectExpression.AddToProjection(column);
continue;
}
column = alias?.TryGetColumnExpression();
if (column != null)
{
column = new ColumnExpression(column.Name, column.Property, subQuery);
alias = new AliasExpression(alias.Alias, column);
selectExpression.AddToProjection(alias);
}
else
{
column = new ColumnExpression(alias.Alias, alias.Expression.Type, subQuery);
selectExpression.AddToProjection(column);
}
}
if (subQuery.OrderBy.Count == 0)
{
subQuery.AddToOrderBy(
new Ordering(new SqlFunctionExpression("@@RowCount", typeof(int)), OrderingDirection.Asc));
}
var columnExpression = new ColumnExpression(RowNumberColumnName, typeof(int), subQuery);
var rowNumber = new RowNumberExpression(columnExpression, subQuery.OrderBy);
subQuery.ClearOrderBy();
subQuery.AddToProjection(rowNumber, false);
Expression predicate = null;
var offset = subQuery.Offset ?? 0;
if (subQuery.Offset.HasValue)
{
predicate = Expression.GreaterThan(columnExpression, Expression.Constant(offset));
}
if (subQuery.Limit.HasValue)
{
var exp = Expression.LessThanOrEqual(columnExpression, Expression.Constant(offset + subQuery.Limit.Value));
if (predicate != null)
{
exp = Expression.AndAlso(predicate, exp);
}
predicate = exp;
}
selectExpression.Predicate = predicate;
return selectExpression;
}