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vbilopav
vbilopav

Posted on • Updated on

postgexecute.net is not ORM

postgexecute.net is lightweight wrapper around NpgsqlConnection object to facilitate simple PostgreSQL execution and data retrieval in .NET Core.

This is NOT an ORM

I repeat:

This is NOT an ORM

  • There is not data conversion whatsoever, and so there is no impedance mismatch issue.

  • All read operations will serialize rows directly and only to IDictionary<string, object>>

or, even much, much better:

This opens up new flexibility options. Now you can:

  • Serialize directly to structure of your choice. No need for extra transformation step. For example dictionary of instances that has key same as your database key.

  • Write directly to stream, json, etc ...

Developer notes

If someone wishes to build micro-ORM Dapper style based on this code base - he or she may freely do so as long as they give proper credits/mentions and link to this repository. And if I may suggest a name - NoORM would be just perfect.

Current version works only with PostgreSQL and there are no plans for now to expand to other databases.

Usage

  • Install PostgExecute.Net or clone this project repo.

  • Two ways to use this API:

1. PostgreSQL connection extensions

Extensions on NpgsqlConnection object (like Dapper).

For example:

using (var connection = new NpgsqlConnection("<connection string>"))
{
    // Execute can be chained. Two chained executes under same connection and/or transaction
    connection.Execute("<pgpsql command 1>").Execute("<pgpsql command 2>");

    // ALL methods not returning any results can be chained

    // Execute another command and read some data and return results
    var myResults1 = connection.Execute("<pgpsql command 3>").Read("<pgpsql read 1>");
    // myResults1 is enumerable of row dictionaries

    // Read into dictionary
    var myResults2 = new List<IDictionary<string, object>>();
    connection.Read("<pgpsql read 2>", result => myResults2.Add(result));

    // Read into custom class
    var myResults3 = List<MyResults>();
    connection.Read("<pgpsql read 3>", r => myResults3.Add(new MyResults{ Field1 = result["field1"] }));

    // etc..
}

2. Static methods

Each extension have same exact version as static method which takes first parameter connection string.

For example:

Postg.Execute("<connection string>", "pgpsql command 1");
Postg.Execute("<connection string>", "pgpsql command 2");
// ...

Notes:

No chaining available because connection is used once and disposed immediatel.

When using static methods PostgreSQL new connection will be created and disposed.

NpgsqlConnection will recycle connection made from same thread (they'll have same PID), but, any pending transaction will be lost and rolled back.

API

Full list of entire available API's and their overloads can be found on this interface definition.

They fall in following three categories:

  1. Execute and ExecuteAsync - Execute PGPSQL command on PostgreSQL database

  2. Single and SingleAsync - Fetch single row from PostgreSQL database

  3. Read and ReadAsync - Read multiple rows from PostgreSQL database

Each version have it async version that ends with Async suffix and they process parameters in same way:

Working with parameters

By convention, parameters on query must start with letter @

Positional parameters

Example:


var result = connection.Single(
    @"select * from (
        select 1 as first, 'foo' as bar, '1977-05-19'::date as day, null as null
    ) as sub
    where first = @1 and bar = @2 and day = @3
    ",
    1, "foo", new DateTime(1977, 5, 19));

Note:

Positional parameters are assigned in order of appearance in query, name is completely irrelevant (but, they must have one).

Named parameters

Unlike positional parameters, when using named parameters - position is irrelevant and every parameter must have unique name.

To accept named parameters interface exposes parameters collection (type NpgsqlParameterCollection) - as lambda parameter:

var result = connection.Single(
    @"select * from (
        select 1 as first, 'foo' as bar, '1977-05-19'::date as day, null as null
    ) as sub
    where first = @1 and bar = @2 and day = @3
    ", p => {
        p.AddWithValue("3", new DateTime(1977, 5, 19));
        p.AddWithValue("2", "foo");
        p.AddWithValue("1", 1);
    });

This API also defines extensions for parameter collection type - that allows chaining. This allows muc mroe elegant syntax:

var result = connection.Single(
    @"select * from (
        select 1 as first, 'foo' as bar, '1977-05-19'::date as day, null as null
    ) as sub
    where first = @1 and bar = @2 and day = @3

    ", p => p.Add("3", new DateTime(1977, 5, 19)).Add("2", "foo").Add("1", 1));

There is also shorter alias named @P:

var result = connection.Single(
    @"select * from (
        select 1 as first, 'foo' as bar, '1977-05-19'::date as day, null as null
    ) as sub
    where first = @1 and bar = @2 and day = @3

    ", p => p.@P("3", new DateTime(1977, 5, 19)).@P("2", "foo").@P("1", 1));

API can also take async version of this lambda:

var result = connection.Single(
    @"select * from (
        select 1 as first, 'foo' as bar, '1977-05-19'::date as day, null as null
    ) as sub
    where first = @1 and bar = @2 and day = @3

    ", async p => {
        await Task.Delay(0); // some async operation...
        p.@P("3", new DateTime(1977, 5, 19)).@P("2", "foo").@P("1", 1);
    });

Fetching the data

Default result set for this API is IDictionary<string, object> for each row:

var result = connection.Single("select 1, 'foo' as bar, '1977-05-19'::date as day, null as null");
// result is `IDictionary<string, object>` that represent result row.

Empty result set will yield empty dictionary.

Note:

There is no data conversion whatsoever (this is not ORM).

null values will NOT have C# null - but DBNull.Value instead.

Reason for this is because your null and database null are not same thing.

Same logic applies for reading multiple rows. Read will return IEnumerable<IDictionary<string, object>>:

var result = connection.Read(
    @"select * from (
    values
        (1, 'foo1', '1977-05-19'::date),
        (2, 'foo2', '1978-05-19'::date),
        (3, 'foo3', '1979-05-19'::date)
    ) t(first, bar, day)");

// result is `IEnumerable<IDictionary<string, object>>`

Read callback lambda

Each read method has version that accepts lambda callback that is executed for each row:

var results = new List<IDictionary<string, object>>();
await connection.Read(
    @"select * from (
    values
        (1, 'foo1', '1977-05-19'::date),
        (2, 'foo2', '1978-05-19'::date),
        (3, 'foo3', '1979-05-19'::date)
    ) t(first, bar, day)",
    result => results.Add(result));

Each version also has lambda overload that have bool as return value.

In that case you can return false to break from iteration immediately and safely:

var results = new List<IDictionary<string, object>>();
connection.Read(
    @"select * from (
    values
        (1, 'foo1', '1977-05-19'::date),
        (2, 'foo2', '1978-05-19'::date),
        (3, 'foo3', '1979-05-19'::date)
    ) t(first, bar, day)",
    result =>
    {
        if ((int)result["first"] == 2)
        {
            return false;
        }
        results.Add(r);
        return true;
    });
// breaks on second row, third is never executed, result will have only one entry

Of course, there is async overload for each API version:

await connection.ReadAsync(@"
        select * from (
        values
            (1, 'foo1', '1977-05-19'::date),
            (2, 'foo2', '1978-05-19'::date),
            (3, 'foo3', '1979-05-19'::date)
        ) t(first, bar, day)",
async result =>
{
    await Task.Delay(0); // some async operation...
    results.Add(result);
});

Tests

Test coverage is 100% and it can be found here

Future plans

When C# 8.0 finally comes out - implement those fancy, ultra fast async streams for read operations supported by C# 8.0 (e.g. async return yield)

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