Precision Java Float in MySQL with JPA (EclipseLink)

Question

I have a precision problem storing a float value in mysql via jpa (EclipseLink). In my code I have annotated the field with

@Column(precision=15, scale=7)
private float x;

But when i store a value like 322,249878 the database returns 322.25. Whats going on there :)?

What is the definition for the column in the db? And if JPA creates the tables, could you get a hold of the DDL? — esej, Jun 19 '12 at 15:05
@esej: the definition for the column is float. The DDL for that colum is X FLOAT as well. — Hans Sperker, Jun 19 '12 at 15:14
Side note: a float cannot contain 15 decimal digits. It is too small. — user207421, Jun 19 '12 at 22:38

score 7 · Accepted Answer · edited May 23 '17 at 11:53

7

precision and scale settings are only applicable to exact numeric types (i.e. BigDecimal in Java and decimal in MySQL).

Floating point types (float and double) are approximate by their nature, therefore these settings don't make sense for them.

Also note that if you change type of this field to BigDecimal you should initialize it with precise values as well.

edited May 23 '17 at 11:53

Community

answered Jun 19 '12 at 15:13

axtavt

Ok thanks for that hint but it doesn't change anything for the precision ;-) – Hans Sperker Jun 19 '12 at 15:17
@jstr: Recheck it. Java type should be `BigDecimal`, MySQL type should be `decimal(15, 7)` (Hibernate will generate it from this annotation if you use schema generation), and field should be initialized by precise value. – axtavt Jun 19 '12 at 15:20
@jstr: Oh, it's EclipseLink, perhaps it behaves differently somehow. – axtavt Jun 19 '12 at 15:22
Ok so now I use BigDecimal which I initialize with Float.toString(x)) and with mit annotation @Column(precision=15, scale=7) the precision is preserved... works for me – Hans Sperker Jun 19 '12 at 15:45

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