c# - 从 Entity Framework Core IQueryable 获取 SQL 代码

Question

我正在使用 Entity Framework Core，我需要查看正在生成哪些 SQL 代码。在 Entity Framework 的早期版本中，我可以使用以下内容:

string sql = ((System.Data.Objects.ObjectQuery)query).ToTraceString();

其中 query 是 IQueryable 对象...但 ToTraceString 在 EF Core 中不可用。

如何在 EF Core 中执行类似的操作？

Answer 1

EF 核心 5/6/网络 5/6

query.ToQueryString()

参见Documentation ToQueryString()和 What's New in EF Core 5.0

var query = _context.Widgets.Where(w => w.IsReal && w.Id == 42);  
var sql = query.ToQueryString();

对于较旧的网络核心框架，可以使用扩展。

核心2.1.2

using System.Linq;
using System.Reflection;
using Microsoft.EntityFrameworkCore.Query;
using Microsoft.EntityFrameworkCore.Query.Internal;
using Microsoft.EntityFrameworkCore.Query.Expressions;
using Microsoft.EntityFrameworkCore.Query.Sql;
using static Microsoft.EntityFrameworkCore.DbLoggerCategory;

    public static class QueryableExtensions
    {
        private static readonly TypeInfo QueryCompilerTypeInfo = typeof(QueryCompiler).GetTypeInfo();
    
        private static readonly FieldInfo QueryCompilerField = typeof(EntityQueryProvider).GetTypeInfo().DeclaredFields.First(x => x.Name == "_queryCompiler");
        private static readonly FieldInfo QueryModelGeneratorField = typeof(QueryCompiler).GetTypeInfo().DeclaredFields.First(x => x.Name == "_queryModelGenerator");
        private static readonly FieldInfo DataBaseField = QueryCompilerTypeInfo.DeclaredFields.Single(x => x.Name == "_database");
        private static readonly PropertyInfo DatabaseDependenciesField = typeof(Database).GetTypeInfo().DeclaredProperties.Single(x => x.Name == "Dependencies");
    
        public static string ToSql<TEntity>(this IQueryable<TEntity> query)
        {
            var queryCompiler = (QueryCompiler) QueryCompilerField.GetValue(query.Provider);
            var queryModelGenerator = (QueryModelGenerator)QueryModelGeneratorField.GetValue(queryCompiler);
            var queryModel = queryModelGenerator.ParseQuery(query.Expression);
            var database = DataBaseField.GetValue(queryCompiler);
            var databaseDependencies = (DatabaseDependencies) DatabaseDependenciesField.GetValue(database);
            var queryCompilationContext = databaseDependencies.QueryCompilationContextFactory.Create(false);
            var modelVisitor = (RelationalQueryModelVisitor) queryCompilationContext.CreateQueryModelVisitor();
            modelVisitor.CreateQueryExecutor<TEntity>(queryModel);
            var sql = modelVisitor.Queries.First().ToString();
    
            return sql;
        }
    }

EF Core 3.0

        public static string ToSql<TEntity>(this IQueryable<TEntity> query)
        {
            using var enumerator = query.Provider.Execute<IEnumerable<TEntity>>(query.Expression).GetEnumerator();
            var enumeratorType = enumerator.GetType();
            var selectFieldInfo = enumeratorType.GetField("_selectExpression", BindingFlags.NonPublic | BindingFlags.Instance) ?? throw new InvalidOperationException($"cannot find field _selectExpression on type {enumeratorType.Name}");
            var sqlGeneratorFieldInfo = enumeratorType.GetField("_querySqlGeneratorFactory", BindingFlags.NonPublic | BindingFlags.Instance) ?? throw new InvalidOperationException($"cannot find field _querySqlGeneratorFactory on type {enumeratorType.Name}");
            var selectExpression = selectFieldInfo.GetValue(enumerator) as SelectExpression ?? throw new InvalidOperationException($"could not get SelectExpression");
            var factory = sqlGeneratorFieldInfo.GetValue(enumerator) as IQuerySqlGeneratorFactory ?? throw new InvalidOperationException($"could not get IQuerySqlGeneratorFactory");
            var sqlGenerator = factory.Create();
            var command = sqlGenerator.GetCommand(selectExpression);
            var sql = command.CommandText;
            return sql;
        }

请参阅 RosiOli 的要点

EF Core 3.1

using System.Linq;
using System.Reflection;
using System.Collections.Generic;
using Microsoft.EntityFrameworkCore.Query.SqlExpressions;
using Microsoft.EntityFrameworkCore.Query;

public static string ToSql<TEntity>(this IQueryable<TEntity> query) where TEntity : class
{
    using var enumerator = query.Provider.Execute<IEnumerable<TEntity>>(query.Expression).GetEnumerator();
    var relationalCommandCache = enumerator.Private("_relationalCommandCache");
    var selectExpression = relationalCommandCache.Private<SelectExpression>("_selectExpression");
    var factory = relationalCommandCache.Private<IQuerySqlGeneratorFactory>("_querySqlGeneratorFactory");

    var sqlGenerator = factory.Create();
    var command = sqlGenerator.GetCommand(selectExpression);

    string sql = command.CommandText;
    return sql;
}

private static object Private(this object obj, string privateField) => obj?.GetType().GetField(privateField, BindingFlags.Instance | BindingFlags.NonPublic)?.GetValue(obj);
private static T Private<T>(this object obj, string privateField) => (T)obj?.GetType().GetField(privateField, BindingFlags.Instance | BindingFlags.NonPublic)?.GetValue(obj);

此问题也由 EF net core team 跟踪并计划在下一个版本中发布。