Use Postgres function to_regclass to check for existence of table (#40)

* Override function to check if table exists

* Fixed whitespace

* Added full function name

---------

Co-authored-by: Aashik Nagadikeri Harish <aashik@StriVR-HQ.local>

Author: aashikgowda

src/Tests/ApprovalFiles/DatabaseSupportTests.VerifyBasicSupport.approved.txt

@@ -1,12 +1,20 @@
 DB Operation: Open connection
 Info:         Beginning database upgrade
 Info:         Checking whether journal table exists
-DB Operation: Execute scalar command: select 1 from INFORMATION_SCHEMA.TABLES where TABLE_NAME = 'schemaversions'
+DB Operation: Execute scalar command: 
+select case
+    when pg_catalog.to_regclass('"schemaversions"') is not null then 1
+    else 0
+end;
 DB Operation: Dispose command
 Info:         Journal table does not exist
 Info:         Executing Database Server script 'Script0001.sql'
 Info:         Checking whether journal table exists
-DB Operation: Execute scalar command: select 1 from INFORMATION_SCHEMA.TABLES where TABLE_NAME = 'schemaversions'
+DB Operation: Execute scalar command: 
+select case
+    when pg_catalog.to_regclass('"schemaversions"') is not null then 1
+    else 0
+end;
 DB Operation: Dispose command
 Info:         Creating the "schemaversions" table
 DB Operation: Execute non query command: CREATE TABLE "schemaversions"

src/Tests/ApprovalFiles/DatabaseSupportTests.VerifyJournalCreationIfNameChanged.approved.txt

@@ -1,12 +1,20 @@
 DB Operation: Open connection
 Info:         Beginning database upgrade
 Info:         Checking whether journal table exists
-DB Operation: Execute scalar command: select 1 from INFORMATION_SCHEMA.TABLES where TABLE_NAME = 'TestSchemaVersions' and TABLE_SCHEMA = 'test'
+DB Operation: Execute scalar command: 
+select case
+    when pg_catalog.to_regclass('"test"."TestSchemaVersions"') is not null then 1
+    else 0
+end;
 DB Operation: Dispose command
 Info:         Journal table does not exist
 Info:         Executing Database Server script 'Script0001.sql'
 Info:         Checking whether journal table exists
-DB Operation: Execute scalar command: select 1 from INFORMATION_SCHEMA.TABLES where TABLE_NAME = 'TestSchemaVersions' and TABLE_SCHEMA = 'test'
+DB Operation: Execute scalar command: 
+select case
+    when pg_catalog.to_regclass('"test"."TestSchemaVersions"') is not null then 1
+    else 0
+end;
 DB Operation: Dispose command
 Info:         Creating the "test"."TestSchemaVersions" table
 DB Operation: Execute non query command: CREATE TABLE "test"."TestSchemaVersions"

src/Tests/ApprovalFiles/DatabaseSupportTests.VerifyVariableSubstitutions.approved.txt

@@ -1,12 +1,20 @@
 DB Operation: Open connection
 Info:         Beginning database upgrade
 Info:         Checking whether journal table exists
-DB Operation: Execute scalar command: select 1 from INFORMATION_SCHEMA.TABLES where TABLE_NAME = 'schemaversions'
+DB Operation: Execute scalar command: 
+select case
+    when pg_catalog.to_regclass('"schemaversions"') is not null then 1
+    else 0
+end;
 DB Operation: Dispose command
 Info:         Journal table does not exist
 Info:         Executing Database Server script 'Script0001.sql'
 Info:         Checking whether journal table exists
-DB Operation: Execute scalar command: select 1 from INFORMATION_SCHEMA.TABLES where TABLE_NAME = 'schemaversions'
+DB Operation: Execute scalar command: 
+select case
+    when pg_catalog.to_regclass('"schemaversions"') is not null then 1
+    else 0
+end;
 DB Operation: Dispose command
 Info:         Creating the "schemaversions" table
 DB Operation: Execute non query command: CREATE TABLE "schemaversions"

src/Tests/ApprovalFiles/NoPublicApiChanges.Run.approved.cs

@@ -64,6 +64,7 @@ public class PostgresqlTableJournal : DbUp.Support.TableJournal
     {
         public PostgresqlTableJournal(System.Func<DbUp.Engine.Transactions.IConnectionManager> connectionManager, System.Func<DbUp.Engine.Output.IUpgradeLog> logger, string schema, string tableName) { }
         protected override string CreateSchemaTableSql(string quotedPrimaryKeyName) { }
+        protected override string DoesTableExistSql() { }
         protected override string GetInsertJournalEntrySql(string scriptName, string applied) { }
         protected override System.Data.IDbCommand GetInsertScriptCommand(System.Func<System.Data.IDbCommand> dbCommandFactory, DbUp.Engine.SqlScript script) { }
         protected override string GetJournalEntriesSql() { }

src/dbup-postgresql/PostgresqlTableJournal.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Data;
 using DbUp.Engine;
 using DbUp.Engine.Output;
@@ -74,4 +74,18 @@ scriptname character varying(255) NOT NULL,
     CONSTRAINT {quotedPrimaryKeyName} PRIMARY KEY (schemaversionsid)
 )";
     }
-}
+
+    /// <inheritdoc/>
+    protected override string DoesTableExistSql()
+    {
+        string fqSchemaTableName = FqSchemaTableName.Replace("'", "''");
+
+        string sql = $@"
+select case
+    when pg_catalog.to_regclass('{fqSchemaTableName}') is not null then 1
+    else 0
+end;";
+
+        return sql;
+    }
+}