.NET9 EFcore支持早期MSSQL数据库 ROW_NUMBER()分页功能

时间：2024-11-27 09:58:03|栏目：ASP.NET|点击：次

前言

NET程序员是很幸福的,MS在上个月发布了NET9.0RTM,带来了不少的新特性,但是呢,还有很多同学软硬件都还没跟上时代的步伐,比如,自己的电脑还在跑Win7,公司服务器还在跑MSSQL2005-2008的!

这不就引入了我们本文要探索的问题,因为MS早在EFcore3.1后就不再内置支持ROW_NUMBER()了,以至于需要兼容分页的代码都需要自行处理,当然同学们如果对EFCore没有依赖度也可以使用其他的ORM选型,当然如果不想折腾EFCore也能使用万能的RawSql拼接执行也是可以的

最近自己发的Nuget包有个国外的程序员朋友提了一个Issue,以至于我马上行动起来

在EFCore9中, 以前兼容的好好的ROW_NUMBER()代码,升级尝鲜后发现跑不起来了,这主要是因为新版本的EFCore9做了很多破坏性更新,以至于我们不得不研究新的底层代码!

兼容实现

之前发布过一个Nuget包,代码主要是基于以前道友兼容EFCore7适配到EFCore8的兼容,代码也不多变化也不大,不过呢,升级到EFCore9后发现底层的API全变了,不得不重新再实现一遍!

以下是兼容EFCore9的代码部分:

#if NET9_0_OR_GREATER
#pragma warning disable EF1001 // Internal EF Core API usage.
namespace Biwen.EFCore.UseRowNumberForPaging;
using Microsoft.EntityFrameworkCore.Query;
using System.Collections.Generic;
public class SqlServer2008QueryTranslationPostprocessorFactory(
    QueryTranslationPostprocessorDependencies dependencies,
    RelationalQueryTranslationPostprocessorDependencies relationalDependencies) : IQueryTranslationPostprocessorFactory
{
    private readonly QueryTranslationPostprocessorDependencies _dependencies = dependencies;
    private readonly RelationalQueryTranslationPostprocessorDependencies _relationalDependencies = relationalDependencies;
    public virtual QueryTranslationPostprocessor Create(QueryCompilationContext queryCompilationContext)
        => new SqlServer2008QueryTranslationPostprocessor(
            _dependencies,
            _relationalDependencies,
            queryCompilationContext);
    public class SqlServer2008QueryTranslationPostprocessor(QueryTranslationPostprocessorDependencies dependencies, RelationalQueryTranslationPostprocessorDependencies relationalDependencies, QueryCompilationContext queryCompilationContext) :
        RelationalQueryTranslationPostprocessor(dependencies, relationalDependencies, (RelationalQueryCompilationContext)queryCompilationContext)
    {
        public override Expression Process(Expression query)
        {
            query = base.Process(query);
            query = new Offset2RowNumberConvertVisitor(query, RelationalDependencies.SqlExpressionFactory).Visit(query);
            return query;
        }
        internal class Offset2RowNumberConvertVisitor(
            Expression root,
            ISqlExpressionFactory sqlExpressionFactory) : ExpressionVisitor
        {
            private readonly Expression root = root;
            private readonly ISqlExpressionFactory sqlExpressionFactory = sqlExpressionFactory;
            private const string SubTableName = "subTbl";
            private const string RowColumnName = "_Row_";//下标避免数据表存在字段
            protected override Expression VisitExtension(Expression node) => node switch
            {
                ShapedQueryExpression shapedQueryExpression => shapedQueryExpression.Update(Visit(shapedQueryExpression.QueryExpression), shapedQueryExpression.ShaperExpression),
                SelectExpression se => VisitSelect(se),
                _ => base.VisitExtension(node)
            };
            private SelectExpression VisitSelect(SelectExpression selectExpression)
            {
                var oldOffset = selectExpression.Offset;
                if (oldOffset == null)
                    return selectExpression;
                var oldLimit = selectExpression.Limit;
                var oldOrderings = selectExpression.Orderings;
                var newOrderings = oldOrderings switch
                {
                    { Count: > 0 } when oldLimit != null || selectExpression == root => oldOrderings.ToList(),
                    _ => []
                };
                var rowOrderings = oldOrderings.Any() switch
                {
                    true => oldOrderings,
                    false => [new OrderingExpression(new SqlFragmentExpression("(SELECT 1)"), true)]
                };
                var oldSelect = selectExpression;
                var rowNumberExpression = new RowNumberExpression([], rowOrderings, oldOffset.TypeMapping);
                // 创建子查询
                IList projections = [new ProjectionExpression(rowNumberExpression, RowColumnName),];
                var subquery = new SelectExpression(
                    SubTableName,
                    oldSelect.Tables,
                    oldSelect.Predicate,
                    oldSelect.GroupBy,
                    oldSelect.Having,
                    [.. oldSelect.Projection, .. projections],
                    oldSelect.IsDistinct,
                    [],//排序已经在rowNumber中了
                    null,
                    null,
                    null,
                    null);
                //构造新的条件:
                var and1 = sqlExpressionFactory.GreaterThan(
                    new ColumnExpression(RowColumnName, SubTableName, typeof(int), null, true),
                    oldOffset);
                var and2 = sqlExpressionFactory.LessThanOrEqual(
                    new ColumnExpression(RowColumnName, SubTableName, typeof(int), null, true),
                    sqlExpressionFactory.Add(oldOffset, oldLimit));
                var newPredicate = sqlExpressionFactory.AndAlso(and1, and2);
                //新的Projection:
                var newProjections = oldSelect.Projection.Select(e =>
                {
                    if (e is { Expression: ColumnExpression col })
                    {
                        var newCol = new ColumnExpression(col.Name, SubTableName, col.Type, col.TypeMapping, col.IsNullable);
                        return new ProjectionExpression(newCol, e.Alias);
                    }
                    return e;
                });
                // 创建新的 SelectExpression，将子查询作为来源
                var newSelect = new SelectExpression(
                    oldSelect.Alias,
                    [subquery],
                    newPredicate,
                    oldSelect.GroupBy,
                    oldSelect.Having,
                    [.. newProjections],
                    oldSelect.IsDistinct,
                    [],
                    null,
                    null,
                    null,
                    null);
                // projectionMapping replace
                var pm = new ProjectionMember();
                var projectionMapping = new Dictionary
                {
                    {
                        pm,
                        oldSelect.GetProjection(new ProjectionBindingExpression(null,pm,null))
                    }
                };
                newSelect.ReplaceProjection(projectionMapping);
                return newSelect;
            }
        }
    }
}
#pragma warning restore EF1001 // Internal EF Core API usage.
#endif