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I´m currently learning about Dapper. I have searched a lot here and other places (including this) and I could not find concrete answers to my doubts:

¿Does Dapper use a generic SQL dialect or it's specific for DB engine? I mean, it uses the SQL syntax expected in the underlaying database engine? At first and after reading over a dozen of examples I thought that the SQL queries where generic, but now trying on PostgresSQL ODBC I have encountered problems with syntax and parameters.

Using this example POCO class ...

public class CardType {

    //Autoincremented Key
    public int Id { get; set; }

    public string Type { get; set; }

    public string Description { get; set; }
}

... the following line does not work for me:

_connection.Execute(@"INSERT cardtypes (type, description) VALUES (@Type,  @Description)", cardType);

First, this line trows an ODBC exception beacuse expects the clause "INTO" before specifying the table. Also the parameters does not work either, because if I'm not wrong, PostgresSQL parameters are setted with the "?" symbol and not with "@keyword". On the GitHub page we can find this:

Dapper has no DB specific implementation details, it works across all .NET ADO providers including SQLite, SQL CE, Firebird, Oracle, MySQL, PostgreSQL and SQL Server.

So I'm lost with this. :) After experimenting a lot I found that putting all the PostgresSQL things works as expected. For example all the next cases worked:

//Manually parameters

var query = @"INSERT INTO cardtypes (type, description) values ('Administrator', 'The Boss')";
_db.Execute(query);


//Dynamic parameters

var dynamicParameters = new DynamicParameters();
dynamicParameters.AddDynamicParams(new {
    cardType.Type,
    cardType.Description
});

var query = @"INSERT INTO cardtypes (type, description) values (?, ?)";    //Note the '?' symbol
_db.Execute(query, dynamicParameters);


//Interpolating values
var query = $@"INSERT INTO cardtypes (type, description) values ('{cardType.Type}', '{cardType.Description}')";
_db.Execute(query);

These previuos cases worked fine. But I'm confused at understanding if the SQL queries are a generic SQL dialect or an specific database engine dialect.

Also I've tried out Dapper.Contrib and fails too with the INSERT statement, for example:

_db.Insert(new CardType() {
    Type = "Administrator",
    Description = "The Boss"
});

It fails too...a weird "[" character exception.

What I'm doing wrong?

My regards!

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1 回答 1

5

Dapper 不会尝试解析您的查询或提供自定义 DSL。而是：它将您的查询直接传递给您选择的 ADO.NET 提供程序。在某些情况下，它确实做了一些调整，但在一般意义上：它没有受到影响。

在 postgresql 的情况下，IIRC 参数是冒号前缀的，而不是 at-prefixed。尝试使用:foo而不是@foo.

于 2016-02-12T18:41:03.630 回答