How to get better table alias names for SQL statements created by Entity Framework?
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21-12-2019 - |
Pergunta
Is it possible to control which table alias names Entity Framework uses for the SQL statements it creates? For example, instead of
SELECT [Extent1].[Id] AS [Id]
FROM [dbo].[Orders] AS [Extend1]
INNER JOIN [dbo].[Customers] AS [Extend2] ON [Extend1].[CustomerId] = [Extend2].[Id]
WHERE [Extent2].[Name] = 'xyz'
I'd like to get
SELECT [order].[Id] AS [Id]
FROM [dbo].[Orders] AS [order]
INNER JOIN [dbo].[Customers] AS [customer] ON [order].[CustomerId] = [customer].[Id]
WHERE [customer].[Name] = 'xyz'
or something similar, as long as I don't have to remember which extend number is which table. Of course in this simple sample it's no problem, but in queries where you have [Extend1]
to [Extend7]
it's really getting complicated.
Solução
You could use IDbCommandInterceptor
and override the CommandText
.
I just created a very simple logic to replace the alias name using regular expression.
Following code
var query = (from f1 in db.Foos
where f1.ParentFooId == null
join f2 in db.Foos on f1.FooId equals f2.ParentFooId
select f2).ToArray();
by default will become something like
SELECT
[Extent1].[FooId] AS [FooId],
[Extent2].[FooId] AS [FooId1],
[Extent2].[FooName] AS [FooName],
[Extent2].[ParentFooId] AS [ParentFooId],
[Extent2].[ParentFoo_FooId] AS [ParentFoo_FooId]
FROM [dbo].[Foos] AS [Extent1]
INNER JOIN [dbo].[Foos] AS [Extent2] ON [Extent1].[FooId] = [Extent2].[ParentFooId]
WHERE [Extent1].[ParentFooId] IS NULL
go
and then I intercepted the command text on ReaderExcecuting
.
public void ReaderExecuting(System.Data.Common.DbCommand command, DbCommandInterceptionContext<System.Data.Common.DbDataReader> interceptionContext)
{
var aliasLookup = new Dictionary<string, string>();
var tableLookup = new Dictionary<string, int>();
var text = command.CommandText;
// Looking something like "[dbo].[Foos] AS [Extent1]"
var pattern = @"\[dbo\]\.\[([\w\d]*)\] AS \[(Extent\d*)\]";
var matches = Regex.Matches(text, pattern);
foreach(Match m in matches)
{
if (m.Groups.Count == 3)
{
var tableName = m.Groups[1].Value;
var aliasName = m.Groups[2].Value;
var replacement = tableName;
if (tableLookup.ContainsKey(tableName)) replacement += tableLookup[tableName]++;
else tableLookup.Add(tableName, 2);
aliasLookup.Add(aliasName, replacement);
}
});
foreach(var pair in aliasLookup)
{
var oldAliasName = string.Format("[{0}]", pair.Key);
var newAliasName = string.Format("[{0}]", pair.Value);
command.CommandText = command.CommandText.Replace(oldAliasName, newAliasName);
}
}
The result would look like
SELECT
[Foos].[FooId] AS [FooId],
[Foos2].[FooId] AS [FooId1],
[Foos2].[FooName] AS [FooName],
[Foos2].[ParentFooId] AS [ParentFooId],
[Foos2].[ParentFoo_FooId] AS [ParentFoo_FooId]
FROM [dbo].[Foos] AS [Foos]
INNER JOIN [dbo].[Foos] AS [Foos2] ON [Foos].[FooId] = [Foos2].[ParentFooId]
WHERE [Foos].[ParentFooId] IS NULL
go
This is just giving you the idea how to do it, the logic hasn't been tested for complex query and it should be used only for debugging.