Catch exception instead of trying to check if the history repository …

…exists (#3294)

Fixes #2878

src/EFCore.PG/Migrations/Internal/NpgsqlHistoryRepository.cs

@@ -75,22 +75,8 @@ private RelationalCommandParameterObject CreateRelationalCommandParameters()
  /// doing so can result in application failures when updating to a new Entity Framework Core release.
  /// </summary>
  protected override string ExistsSql
- {
- get
- {
- var stringTypeMapping = Dependencies.TypeMappingSource.GetMapping(typeof(string));
-
- return
- $"""
-SELECT EXISTS (
- SELECT 1 FROM pg_catalog.pg_class c
- JOIN pg_catalog.pg_namespace n ON n.oid=c.relnamespace
- WHERE n.nspname={stringTypeMapping.GenerateSqlLiteral(TableSchema ?? "public")} AND
- c.relname={stringTypeMapping.GenerateSqlLiteral(TableName)}
-)
-""";
- }
- }
+ => throw new UnreachableException(
+ "We should not be checking for the existence of the history table, but rather creating it and catching exceptions (see below)");
 
  /// <summary>
  /// This is an internal API that supports the Entity Framework Core infrastructure and not subject to
@@ -194,6 +180,58 @@ public override string GetEndIfScript()
 END $EF$;
 """;
 
+ /// <summary>
+ /// Calls the base implementation, but catches "table not found" exceptions; we do this rather than try to detect whether the
+ /// migration table already exists (see <see cref="ExistsAsync" /> override below), since it's difficult to reliably check if the
+ /// migration history table exists or not (because user may set PG <c>search_path</c>, which determines unqualified tables
+ /// references when creating, selecting).
+ /// </summary>
+ public override IReadOnlyList<HistoryRow> GetAppliedMigrations()
+ {
+ try
+ {
+ return base.GetAppliedMigrations();
+ }
+ catch (PostgresException e) when (e.SqlState is "3D000" or "42P01")
+ {
+ return [];
+ }
+ }
+
+ /// <summary>
+ /// Calls the base implementation, but catches "table not found" exceptions; we do this rather than try to detect whether the
+ /// migration table already exists (see <see cref="ExistsAsync" /> override below), since it's difficult to reliably check if the
+ /// migration history table exists or not (because user may set PG <c>search_path</c>, which determines unqualified tables
+ /// references when creating, selecting).
+ /// </summary>
+ public override async Task<IReadOnlyList<HistoryRow>> GetAppliedMigrationsAsync(CancellationToken cancellationToken = default)
+ {
+ try
+ {
+ return await base.GetAppliedMigrationsAsync(cancellationToken).ConfigureAwait(false);
+ }
+ catch (PostgresException e) when (e.SqlState is "3D000" or "42P01")
+ {
+ return [];
+ }
+ }
+
+ /// <summary>
+ /// Always returns <see langword="true" /> for PostgreSQL - it's difficult to reliably check if the migration history table
+ /// exists or not (because user may set PG <c>search_path</c>, which determines unqualified tables references when creating,
+ /// selecting). So we instead catch the "table doesn't exist" exceptions instead.
+ /// </summary>
+ public override bool Exists()
+ => true;
+
+ /// <summary>
+ /// Always returns <see langword="true" /> for PostgreSQL - it's difficult to reliably check if the migration history table
+ /// exists or not (because user may set PG <c>search_path</c>, which determines unqualified tables references when creating,
+ /// selecting). So we instead catch the "table doesn't exist" exceptions instead.
+ /// </summary>
+ public override Task<bool> ExistsAsync(CancellationToken cancellationToken = default)
+ => Task.FromResult(true);
+
  private sealed class NpgsqlMigrationDatabaseLock(IHistoryRepository historyRepository) : IMigrationsDatabaseLock
  {
  /// <summary>