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Signum Framework Tutorials Part 2 – Southwind Logic

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15 Nov 2012LGPL325 min read 31.2K   1K   22  
In this part, we will focus on writing business logic, LINQ queries and explain inheritance
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text;
using Signum.Utilities;
using Signum.Utilities.ExpressionTrees;
using Signum.Entities.DynamicQuery;

namespace Signum.Engine.Linq
{
    internal class RowNumberFiller : DbExpressionVisitor
    {
        static internal Expression Fill(Expression expression)
        {
            return new RowNumberFiller().Visit(expression);
        }

        SourceExpression innerSource;

        protected override Expression VisitSelect(SelectExpression select)
        {
            Expression top = this.Visit(select.Top);
            SourceExpression from = this.VisitSource(select.From);
            Expression where = this.Visit(select.Where);

            SourceExpression last = innerSource;
            innerSource = from; 

            ReadOnlyCollection<ColumnDeclaration> columns = this.VisitColumnDeclarations(select.Columns);

            innerSource = last;

            ReadOnlyCollection<OrderExpression> orderBy = this.VisitOrderBy(select.OrderBy);
            ReadOnlyCollection<Expression> groupBy = this.VisitGroupBy(select.GroupBy);

            if (top != select.Top || from != select.From || where != select.Where || columns != select.Columns || orderBy != select.OrderBy || groupBy != select.GroupBy)
                return new SelectExpression(select.Alias, select.Distinct, select.Reverse, top, columns, from, where, orderBy, groupBy);

            return select;
        }

        protected override Expression VisitRowNumber(RowNumberExpression rowNumber)
        {
            if (rowNumber.OrderBy == null || rowNumber.OrderBy.IsEmpty())
            {
                SelectExpression inner = (SelectExpression)innerSource;

                var cols = inner.Columns.Select(cd => new OrderExpression(OrderType.Ascending, cd.GetReference(inner.Alias)));

                return new RowNumberExpression(cols.ToReadOnly());
            }

            return base.VisitRowNumber(rowNumber);
        }
    }
}

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License

This article, along with any associated source code and files, is licensed under The GNU Lesser General Public License (LGPLv3)


Written By
Software Developer (Senior) Signum Software
Spain Spain
I'm Computer Scientist, one of the founders of Signum Software, and the lead developer behind Signum Framework.

www.signumframework.com

I love programming in C#, Linq, Compilers, Algorithms, Functional Programming, Computer Graphics, Maths...

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