How To Access SQL Generated By Entity Framework Core 3

July 28, 2020
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How To Access SQL Generated By Entity Framework Core 3
[DISPLAY_ULTIMATE_SOCIAL_ICONS] Entity Framework Core (EF) converts expressions into SQL at runtime. In earlier versions, it was straight forward to get the SQL. In Entity Framework Core 3, you must access the SQL using ILogger. This article explains how to access the SQL generated and gives some example code to access the output of queries made behind the scenes. This article works with Entity Framework Core 3. Note: Microsoft is about to release Entity Framework Core 5 soon. This version will have an easier method to get at the SQL. This is the interface method. Many developers may feel uncomfortable if they do not know what SQL EF executes behind the scenes. There's a good reason for this! Expressions may not map on to SQL very easily. You may end up executing SQL that doesn't take advantage of indexes, or the expression may end up filtering records after the data was selected from the database. In older versions of EF you could use ToTraceString()but this no longer exists in EF Core 6. There may even be other reasons to access the SQL. Perhaps your want to convert EF expressions to SQL. This is all possible in EF Core. Grab the full sample here. The Basics The key to making entity framework log SQL queries is to provide it with a logging factory: optionsBuilder.UseLoggerFactory(_loggerFactory); And, the factory must have a filter like so: var loggerFactory = LoggerFactory.Create(builder => { builder .AddFilter((category, level) => category == DbLoggerCategory.Database.Command.Name && level == LogLevel.Information); }); That's it. If you add console logging, SQL will be logged to the console when the SQL executes. var loggerFactory = LoggerFactory.Create(builder => { builder .AddConsole((options) => { }) .AddFilter((category, level) => category == DbLoggerCategory.Database.Command.Name && level == LogLevel.Information); }); This is an example query: using (var ordersDbContext = new OrdersDbContext(loggerFactory)) { var orderLines = ordersDbContext.OrderLines.Where(o => o.Id == Guid.Empty).ToList(); orderLines = ordersDbContext.OrderLines.ToList(); } This is the console output: info: Microsoft.EntityFrameworkCore.Database.Command[20101]Executed DbCommand (3ms) [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT COUNT(*) FROM sqlite_master WHERE type = 'table' AND rootpage IS NOT NULL;info: Microsoft.EntityFrameworkCore.Database.Command[20101]Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT o.Id, o.Count, o.ItemFROM OrderLines AS oWHERE o.Id = '00000000-0000-0000-0000-000000000000'info: Microsoft.EntityFrameworkCore.Database.Command[20101]Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT o.Id, o.Count, o.ItemFROM OrderLines AS o Incidentally, it looks as though the where clause is not parameterized. Is this a security hole in Entity Framework Core for SQLite? Here is some further documentation on this approach. Getting More Detail You may need more detail. Or, you may want to use EF to generate SQL for some reason. You can achieve that with this code. This is an implementation of ILogger that will allow you to hook into an action when SQL runs. public class EntityFrameworkSqlLogger : ILogger { #region Fields Action<EntityFrameworkSqlLogMessage> _logMessage; #endregion #region Constructor public EntityFrameworkSqlLogger(Action<EntityFrameworkSqlLogMessage> logMessage) { _logMessage = logMessage; } #endregion #region Implementation public IDisposable BeginScope<TState>(TState state) { return default; } public bool IsEnabled(LogLevel logLevel) { return true; } public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter) { if (eventId.Id != 20101) { //Filter messages that aren't relevant. //There may be other types of messages that are relevant for other database platforms... return; } if (state is IReadOnlyList<KeyValuePair<string, object>> keyValuePairList) { var entityFrameworkSqlLogMessage = new EntityFrameworkSqlLogMessage ( eventId, (string)keyValuePairList.FirstOrDefault(k => k.Key == commandText).Value, ...

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