I am passing a map to MyBatis with some parameters. Now these parameters are based on the incoming JSON request... So the numbers of parameters are variable.
So sometimes it can happen that some parameter is not coming in that case MyBatis throws BindingException in the null check itself ... What is the suggested way to handle this kind of scenario.
Related
The below line is from the doc : https://mybatis.org/mybatis-3/configuration.html#:~:text=Whenever%20MyBatis%20sets%20a%20parameter,and%20Time%20API)%20by%20default.
Whenever MyBatis sets a parameter on a PreparedStatement or retrieves a value from a ResultSet, a TypeHandler is used to retrieve the value in a means appropriate to the Java type.
Also, we can override the type handlers or create our own to deal with unsupported or non-standard types.
So, one such scenario I have seen is for Json Type where we need custom TypeHandler since Json type is not supported by mybatis. Is my understanding correct ?
Also, I want to know few other types which isnot supported by mybatis (just curious), I searched on net but couldnot find anything relavent.
When we use Mybatis , in <select> ...</select> statment I know we need set jdbcType beacuse the IN variable maybe null, but when I see the document of Mybatis, I found jdbcType in <result>...</result> under ResultMap. the document of the
jdbcTpe in <result>...</result> was:
... The JDBC type is only required for nullable columns upon insert, update or delete. This is a JDBC requirement, not a MyBatis one. So even if you were coding JDBC directly, you'd need to specify this type – but only for nullable values.
the bold word say only required for nullable columns upon insert, update or delete.
BUT,the element of result is used in select neither insert, update or delete.
so ,is it necessary use jdbcType in <result>...</result> ?
Most of the time, no. Why? Read on.
If you want to use a null as a JDBC parameter value you need to specify the jdbcType. That's a restriction of the JDBC specification you can't avoid. Therefore, if there's even a remote possibility a JDBC parameter could have a null value, then yes, specify it.
This does not apply to parameters preprocessed by MyBatis inside MyBatis tags, like the ones you use in the "test" attribute of the < if > tag. Those ones are not JDBC parameters.
Now, for the columns you read. These are the ones you are interested on. The thing is most of the time you don't need them. MyBatis will pick the right JDBC type for you. Well... this has been the case for me 99.999% of the time.
What about the other 0.001%? For some exotic column types -- that you rarely use -- MyBatis may pick the wrong JDBC type for you. The designers of MyBatis thought about this case, and give you the chance of overriding it. I think I remember an XML type database column that MyBatis was unsuccessfully trying to read as a VARCHAR, but I don't remember which database.
Bottom line, don't use it when reading columns, unless MyBatis reads exotic data type columns (XML, UUID, POINT, etc.) the wrong way.
When I tried to get some values in a DataFrame, like:
df.select("date").head().get(0) // type: Any
The result type is Any, which is not expected.
Since a dataframe contains the schema of the data, it should know the DataType for each column, so when i try to get a value using get(0), it should return the value with the correct type. However, it does not.
Instead, I need to specify which DataType i want using getDate(0), which seems weird, inconvenient, and makes me mad.
When I have specified the schema with the correct DataTypes for each column when i created the Dataframe, I don't want to use different getXXX()' for differentcolumn`s.
Are there some convenient ways that I can get the values with their own correct types? That is to say, how can I get the values with the correct DataType specified in the schema?
Thank you!
Scala is a statically typed language. so the get method defined on the Row can only return values with a single type because the return type of the get method is Any. It cannot return Int for one call and a String for another.
you should be calling the getInt, getDate and other get methods provided for each type. Or the getAs method in which you can pass the type as a parameter (for example row.getAs[Int](0)).
As mentioned in the comments other options are
use Dataset instead of a DataFrame.
use Spark SQL
You can call the generic getAs method as getAs[Int](columnIndex), getAs[String](columnIndex) or use specific methods like getInt(columnIndex), getString(columnIndex).
Link to the Scaladoc for org.apache.spark.sql.Row.
How does Slick handle a query that returns multiple result sets?
For example, if I wanted to retrieve information about a table using sp_help someTableName
Which would return a number of result sets. I can get the first result set, simply using scala.slick.jdbc.StaticQuery.queryNA[Tuple4[String, String, String,String]]("sp_help tblInbox_membership").first()
How do I get the second result set?
You must be using Sybase or maybe SqlServer.
I'm not familiar with Slick (yet), but the way to access subsequent ResultSets from a statement in JDBC is to call Statement.getMoreResults(), then if that succeeds Statement.getResultSet(). Slick gives you a Statement object with Session.withStatement, so you could at least use the JDBC api to get your resultsets, or feed the ResultSet to Slick if there is a way to do that.
I am using JPA native query to call a stored procedure and map the return result to a class
createNativeQuery(String sqlString, Class resultClass);
Here sqlString is a stored procedure in this format:
{call storeProcedureName parameter1, paramter2, parameter3}
I noticed that when one of the parameter contains a forward slash (/), the result result will be wrong. Has any body encountered this problem before and how to solve it? thanks
I am using EclipseLink and glassfish server.
Are you in-lining the parameters into your SQL, or using parameters on your query? You should use parameters on your query, in-lining parameters into SQL is very bad (can lead to SQL injection attacks).
See,
http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Querying/Native#Parameters