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,我们是不是还有很多同学软硬件都还没更上,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!
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EFcore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程序员兼容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;
using System.Reflection;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private const string _mp = "_projectionMapping";private static readonly FieldInfo ProjectionMapping = typeof(SelectExpression).GetField(_mp, BindingFlags.NonPublic | BindingFlags.Instance);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<ProjectionExpression> 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);//使用反射替换_projectionMapping变量:ProjectionMapping.SetValue(newSelect, ProjectionMapping.GetValue(oldSelect));return newSelect;}}}
}#pragma warning restore EF1001 // Internal EF Core API usage.
#endif
最后
实现上逻辑还是一致的,反正都是将Offset转换为ROW_NUMBER()子查询中,取行号数据
只是代码实现区别有一些,以前的EFCore底层代码很多已经不在可用比如直接使用PushdownIntoSubquery()会报错,GenerateOuterColumn()内部的扩展方法发生了破坏性更新导致不能再使用等!
如果你的程序需要升级到NET9并还在使用早期数据库的话,可以引用我实现的代码部分
代码我放在了,任何问题欢迎Issue https://github.com/vipwan/Biwen.EFCore.UseRowNumberForPaging
