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In-Reply-To: <f8b65955-50fb-a561-6cd0-7d98861103d1@dalibo.com>
From: Daniel Fortunov <postgresql@danielfortunov.com>
Date: Mon, 8 Feb 2021 22:38:10 +0000
Message-ID: 
 <CAH1rg6b41jgi2A7qOaUGx1KwkuzD3hNMFWwfcQPKb1Oy5FGVRQ@mail.gmail.com>
Subject: Re: Latest developments in psycopg3
To: Denis Laxalde <denis.laxalde@dalibo.com>
Cc: Daniele Varrazzo <daniele.varrazzo@gmail.com>, psycopg@postgresql.org
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>
> > 1) We can provide a feature to select the type of cursor that is not
> > much dissimilar from psycopg2
> > 2) Do we need DictCursor/RealDictCursor? ISTM that one of the two
> > would be sufficient? Possibly an object inheriting from a Python dict
> > instead of emulating it so that e.g. json.dumps()
>
> Inheriting from dict is strange because we only need read access. So
> rather collections.abc.Mapping, I think.
>

One advantage of using a real dict is that it leaves the door open for the
caller to mutate the results as they consume them. A little impure, I know,
but one practical example I can think of would be where you want to augment
your results with additional data (coming from a different source, outside
the database).

RealDictCursor gives you the flexibility to do this, whereas
collections.abc.Mapping would force you to construct a new dict instance
for every row in order to get the same result.

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<div dir=3D"ltr"><div class=3D"gmail_quote"><blockquote class=3D"gmail_quot=
e" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204)=
;padding-left:1ex">&gt; 1) We can provide a feature to select the type of c=
ursor that is not<br>
&gt; much dissimilar from psycopg2<br>
&gt; 2) Do we need DictCursor/RealDictCursor? ISTM that one of the two<br>
&gt; would be sufficient? Possibly an object inheriting from a Python dict<=
br>
&gt; instead of emulating it so that e.g. json.dumps()<br>
<br>
Inheriting from dict is strange because we only need read access. So <br>
rather collections.abc.Mapping, I think.<br></blockquote><div>=C2=A0</div><=
div>One advantage of using a real dict is that it leaves the door open for =
the caller to mutate the results as they consume them. A little impure, I k=
now, but one practical example I can think of would be where you want to au=
gment your results with additional data (coming from a different source, ou=
tside the database).</div><div><br></div><div>RealDictCursor gives you the =
flexibility to do this, whereas collections.abc.Mapping would force you to =
construct a new dict instance for every row in order to get the same result=
.</div></div></div>

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