如何從 Entity Framework Core IQueryable 取得 SQL 程式碼？

從Entity Framework Core IQueryable 取得SQL 程式碼

從Entity Framework Core 的IQueryable 產生SQL 程式碼的任務與先前版本的Entity Framework 相符比，在EF Core 中處理物件需要採取稍微不同的方法。

EF Core 5/6 (Net 5/6)

在EF Core 5 及更高版本中，您可以使用ToQueryString() 方法來擷取SQL 程式碼：

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

Core 2.1.2 和早期

對於早期版本的EF Core（2.1.2 及更低版本），您可以利用擴充方法來實現此目的：

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;
        }
    }</tentity></tentity></tentity>

EF Core 3.0

中EF Core 3.0，需要不同的擴充方法：

        public static string ToSql<tentity>(this IQueryable<tentity> query)
        {
            using var enumerator = query.Provider.Execute<ienumerable>>(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;
        }</ienumerable></tentity></tentity>

EF Core 3.1

在EF Core 3.1中，還需要另一種擴展方法：

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>>(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);</t></iquerysqlgeneratorfactory></selectexpression></ienumerable></tentity></tentity>

值得注意的是，開發團隊已經意識到了這一限制，併計劃在未來的版本中解決它。

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